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Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/standardizingamaOOcran 


STANDARDIZING 

THE 

AMALGAM 
F\  LUNG 

BY 

WALTER  G.CRANDALL,D.D.S. 

SECOND  EDITION 


PUBLISHED  BY 

THE  CLEVELAND  DENTAL  MFG.  CO. 

CLEVELAND,  OHIO.  U.  S.  A. 


Copyright  1915-1916 

by 

The  Cleveland  Dental  Mfg.  C< 

Cleveland,  Ohio,  U.  S.  A. 


standardizing  the  Amalgam  Filling 

Second  Edition 


THE  enthusiastic  reception  accorded  by  the  dental  profession 
to  the  first  issue  of  "Standardizing  the  Amalgam  Filling," 
adds  to  our  pleasure  in  presenting  the  second  edition.  The 
need  for  a  simple  and  comprehensive  treatment  of  the  subject  of 
amalgam  manipulation  has  been  revealed  by  this  enthusiasm  and 
we  believe  that  a  real  appreciation  of  the  importance  of  amalgam 
restorations,  as  a  factor  in  conserving  the  teeth  and  health  of 
patients,  has  resulted  from  this  publication. 

The  present  edition  of  ''Standardizing  the  Amalgam  Filling" 
has  been  revised  in  the  interest  of  unity  and  convenient  reference 
and  some  of  the  results  of  research  in  metals,  made  by  a  highly 
competent  metallographist  at  Yale,  Sheffield  Scientific  School, 
have  been  added.  This  work,  which  represents  the  first  intensive 
use  of  metallography  applied  to  dental  alloys,  has  been  done  under 
the  direction  of  Dr.  Crandall  and  will  be  reported  fully  in  a  later 
publication. 

To  those  who  have  gone  before  us  in  the  investigation  of  the 
alloy  metals  and  methods  of  combining  them,  we  offer  our  acknowl- 
edgments. The  best  of  the  past  has  been  combined  with  research 
and  increased  practical  experience  in  the  evolution  of  the  Crandall 
Method  of  Amalgam  Restoration.  It  is  offered  to  the  profession 
with  the  assurance  that  it  is  founded  upon  scientific  principles  and 
that  its  application,  under  varying  conditions  of  practice  will  result 
in  a  step  in  advance  of  present  methods  in  the  restoration  of 
bicuspid  and  molar  teeth. 


THE  CLEVELAND  DENTAL 
MANUFACTURING  COMPANY 


ZW  the  friends  and  confreres 
who  have  assisted  me  in  the 
experiments  necessary  to  this 
work,  to  those  who  have  offered 
criticism  and  suggestion.  I 
ivish  to  express  my  heartfelt 
and  sincere  gratitude.  The  list 
of  those  icho  have  disinterest- 
edly aided  in  this  work  has 
grown  to  such  proportions  that 
it  seems  impossible  to  partic- 
ularize here.  It  is  a  pleasure 
to  acknowledge  my  indebtedness 
to  these  men  and  I  offer  to  each 
and  every  one  my  heartiest 
appreciation. 

TF.  C.  C  RAX  BALL. 


standardizing  the  Amalgam  Filling 


By  Walter  G.  CrandaU,  D.  D.  S. 


THE  earliest  use  of  amalgam  as  a 
material  for  restoring  portions  of  the 
human  teeth  is  of  comparatively  re- 
cent date.  It  is  probably  well  within  the 
past  century  that  it  was  first  employed  and 
within  half  a  century  that  its  use  has  become 
at  all  common.  Many  men  who  are  stiU 
active  in  the  practice  of  dentistry  recall  very 
vividly  the  contention  over  the  material 
when  its  introduction  was  first  becoming 
general  throughout  this  country  as,  at  that 
time,  amalgam  was  in  such  ill  repute  that 
its  use  by  any  dentist  was  sufficient  to  bar 
him  from  membership  in  the  dental  societies 
which  then  existed,  and  from  any  associ- 
ation with  his  confreres. 

However,  it  is  not  the  intent  of  this 
article  to  discuss  the  amalgam  of  the  past, 
but  the  amalgam  of  the  present,  and  its 
possibilities.  The  importance  of  any  mate- 
rial bears  a  direct  relation  to  the  extent  of 
its  use.  Judged  from  this  standpoint,  the 
importance  of  amalgam  is  at  once  evident, 
for  a  comparison  of  the  number  of  amalgam 
fillings  inserted  with  all  fillings  of  other 
materials,  when  taken  from  records  of 
actual  practice,  has  always  shown  at  least 
seventy -five  per  cent  of  the  total  to  be 
amalgam. 

In  reviewing  any  scientific  research  of 
dental  amalgams  and  amalgam  alloys, 
acknowledgment  must  be  made  of  the  work 
done  in  this  field  by  Greene  Vardiman  Black. 
If  he  had  given  nothing  else  to  the  advance- 
ment of  the  dental  profession,  his  name 
should  still  be  held  in  grateful  remembrance 
for  his  investigation  and  classification  of 
the  minute  actions  of  the  dental  amalgam 
alloy  metals.  Two  decades  have  passed 
and  we  are  only  beginning  to  appreciate  the 


heritage  that  is  ours  through  his  efforts  and 
to  realize  that  we  have  failed,  in  some  par- 
ticulars, to  take  advantage  of  the  work 
which  should  have  given  us  an  unalterable 
standard  for  dental  amalgam  alloys. 

The  cKnical  experience  of  the  past  has 
taught  us  the  value  of  amalgam  and  has 
demonstrated  its  wonderful  tooth-saving 
quafities,  even  when  it  has  been  used  in  a 
careless,  indifferent  manner.  Too  often  it 
has  been  considered  only  as  a  cheaper  sub- 
stitute for  the  patient  who  can  not  afford, 
or  will  not  have,  a  gold  filling,  inlay,  or 
crown,  and  the  work  has  been  done  with 
little  care  in  the  preparation  of  the  cavity, 
with  a  plastic  alloy,  and  without  regard 
to  the  restoration  of  anatomical  form  or 
occlusion,  simply  as  the  quickest  means  of 
getting  rid  of  the  patient.  It  is  possible, 
however,  to  save  teeth  with  amalgam  when 
it  has  become  practically  an  impossibility 
to  save  them  with  other  materials. 

Now  and  then  we  have  all  seen  cases  in 
which  amalgam  fillings  have  given  more 
than  ordinary  service,  proving  the  inherent 
value  of  the  material.  The  more  frequent 
failures  show  us  the  lack  of  a  standardized 
technic  for  amalgam  work.  Notwithstand- 
ing the  more  and  more  frequent  discussions 
of  the  subject,  do  we  really  know  the  req- 
uisite qualities  of  a  dental  amalgam  alloy; 
in  what  proportions  it  should  be  combined 
with  mercury;  whether  or  not  the  cavity 
should  have  a  cement  lining  for  amalgam; 
how  much  force  is  required  to  condense 
amalgam;  the  form  and  size  of  instruments 
best  adapted  for  this  purpose;  the  modi- 
fications of  Black's  cavity  preparation  for 
gold  foil  which  are  permissible  or  advisable 
for  amalgam;  the  method  of  alloying  which 


[6] 


STANDARDIZING         THE         AMALGAM         FILLING 


will  produce  a  dental  amalgam  alloy  with 
the  most  desirable  qualities? 

It  is  the  purpose  of  this  article  to  bring 
before  you.  as  plainly  and  emphaticall}'  as 


possible,  the  essentials  of  a  standardized 
technic  for  amalgam  restoration.  A  clear 
and  systematic  presentation  of  the  subject  re- 
quires the  following  subdivision  into  sections : 


Essentials  of  Standardized  Amalgam  Technic  Classified 

I.  Proper  Cavity  Preparation 

II.  Accurately  Tested  Alloys  of  the  Greatest  Strength  and  Stability 

III.  Correct  Amalgamation 

IV.  Correct  Instrumentation  and  Condensation 

V.     Correct  Contour  and  Finish  of  the  Restoration 
\l.     Profitable  Fees 

Section  I — Cavity  Preparation 


SCIENTIFIC  cavity  preparation  is  as 
essential  for  amalgam  as  for  a  filling  of 
any  other  material.  Without  proper  prep- 
aration of  the  cavity,  no  filling  material  is 
given  a  just  opportunity  to  prove  its  worth, 
and  the  writer  is  inclined  to  beheve  that  the 
lack  of  such  preparation  is  the  most  fre- 
quent cause  of  failure  of  amalgam  fillings. 

The  entire  preparation  of  the  cavity 
should  bear  a  distinct  relation  to  the  condi- 
tions which  surround  the  tooth.  We  should 
study  conditions,  observe,  if  possible,  the 
faulty  condition  which  produced  the  lesion, 
and  attempt  to  remedj'  this,  producing  an 
environment  which  wiU  prevent  the 
recurrence  of  the  pathological  state.  We 
should  study  the  occlusion  and  build  to 
withstand  its  existing  force  and,  if  possible, 
to  anticipate  future  developments.  The 
restoration  of  a  tooth  is  a  surgical  procedure 
and  requires  expert  knowledge  in  diagnosing 
and  planning.  The  completed  restoration 
should  be  fuUy  visuahzed  and  decided 
upon  before  the  operation  is  begun. 

The  writer  would  adA^ise  those  who  wish 
exhaustive  information  on  the  subject  of 
ca\'ity  preparation  to  make  a  close  study  of 


Black's  "Operative  Dentistr}-"  or  to  take  a 
course  of  chnical  instruction  from  some 
master  of  Dr.  Black's  scientific  system.  It 
is  impossible  to  consider  the  subject  ade- 
quately within  the  limits  of  the  present 
article,  but  we  shall  consider  brieflj'  several 
forms  of  cavities  occurring  most  commonly 
in  bicuspid  and  molar  teeth.  Its  color 
limits  the  use  of  amalgam  almost  entirely 
to  these  teeth. 

In  the  main,  cavity  preparation  for  amal- 
gam should  be  the  same  as  for  gold.  The 
ideal  ca^'it^'  is  a  box  form  ^-ith  a  flat  base 
and  walls  at  right  angles  to  the  base.  This, 
of  course,  becomes  complicated  in  many 
forms  of  ca\TLties,  but  the  principle  should 
be  followed  in  any  cavity  where  stress  will 
be  apphed  to  the  completed  filHng. 

Dr.  Black  gives  the  following  as  the  order 
of  procedure  in  cavity  preparation: 

1.  Obtain  the  required  outline  form. 

2.  Obtain  the  required  resistance  form. 

3.  Obtain  the  required  retention  form. 

4.  Obtain  the  required  convenience  form. 

5.  Remove  am-  remaining  carious  dentin. 

6.  Finish  the  enamel  walls. 

7.  IMake  the  toilet  of  the  cavity. 


CAVITY        PREPARATION         FOR        AMALGAM 


We  shall  consider  briefly  these  various 
steps,  noting  especially  variations  from  the 
usual  procedure  for  gold  foil. 

1 — Outline  Form 

This  form  is  the  outline  of  the  cavity  upon 
the  enamel  surface;  it  must  be  such  that  it 
will  place  all  of  the  margins  in  areas  which  are 
comparatively  immune  to  initial  decay. 

For  cavities  on  proximal  surfaces,  the 
gingival  wall  of  the  cavity  should  be  just 
beneath  the  free  margin  of  the  gum,  as 
decay  rarely,  if  ever,  begins  at  this  point 
when  the  tissue  is  in  a  healthy  condition. 
When  the  gum  has  receded  upon  the  root, 


Figure  1  shows  an  upper  molar  with  cavity 
preparation  for  amalgam  on  the  disto- 
occlusal  surfaces.  The  outline  form  of  this 
cavity  includes  all  of  the  area  of  the  distal 
surface  which  is  susceptible  to  decay.  The 
buccal  and  Ungual  walls  are  at  right 
angles  to  the  base  of  the  cavity,  with 
flat  base  on  the  gingival  and  pulpal  walls. 

it  will  be  quite  useless,  of  course,  to  attempt 
to  place  the  gingival  margin  in  such  an  area. 

The  buccal  and  lingual  margins  must  be 
so  placed  in  the  embrasures  that  food  will 
sweep  over  and   cleanse  them,   making  it 


impossible  for  plaques  of  bacteria  to  form 
and  institute  a  new  area  of  decay. 

Upon  the  occlusal  surface,  under  usual 
conditions,  the  outline  form  should  include 
that  portion  of  the  occlusal  surface  which  is 
contiguous  to  the  cavity  and  should  be 
extended  to  include  all  fissures  susceptible 
to  future  decay. 

Where  the  occlusal  and  proximal  portions 
of  the  cavity  join,  the  cavity  should  be  cut 
as  broad  as  conditions  will  permit,  as  shown 
in  Figure  1,  A-B.  Care  should  be  taken  not 
to  approach  too  near  the  summit  of  the 
cusps,  where  the  enamel  rods  lie  in  a  direc- 
tion which  will  cause  inferior  margins,  and 
not  to  cut  too  deeply  into  the  dentin,  as 
the  horns  of  the  pulp  often  extend  to  a 
point  where  they  are  easily  involved. 
Especial  emphasis  should  be  placed  upon 
the  broad  outline  at  this  point  as  the  narrow 
connection  between  the  occlusal  and  prox- 
imal portions  of  a  cavity  is  a  fault  common 
to  many  operators.  The  broad  outhne  will 
give  strength  to  the  restoration,  where 
strength  is  most  needed,  by  allowing  a 
greater  bulk  of  amalgam  to  be  placed  at 
this  point.  Amalgam  is  not  a  ductile  mate- 
rial and  continued  heavy  stress  upon  a 
small  body  of  it  will  surely  cause  it  to  give 
way  in  time;  its  strength  increases  rapidly 
as  its  bulk  increases.  We  must  constantly 
bear  in  mind  the  physical  properties  of 
amalgam  and  adapt  our  methods  to  its 
quaUties  to  obtain  permanent  results. 

If  decay  has  progressed  throughout  the 
dentin  so  that  any  cusp  has  become  under- 
mined or  weakened,  the  cusp  should  be 
cut  away,  for  at  least  one-third  of  the 
occluso-gingival  diameter  of  the  tooth,  so 
that  it  may  be  restored  with  a  bulk  of 
amalgam.  Representative  cases  in  which  this 
has  been  done  are  shown  in  Figures  2,  3,  4 
and  5.     The  wall,  in  each  case,  has  been 


[7] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


reduced  with  a  stone  and  beveled  so  that 
the  reproduction  with  amalgam  will  lock 
the  cusp  and  prevent  fracture. 

Verj'  often  decay  has  become  extensive 
from  both  the  mesial  and  distal  surfaces  and 
all  the  cusps  are  more  or  less  undermined. 


Figure  2  shows  a  cavity  preparation  for 
amalgam  in  an  upper  bicuspid.  In  this 
case  there  were  extensive  cavities  upon 
both  the  mesial  and  distal  surfaces  to  such 
an  extent  that  the  Ungual  cusp  had  become 
weakened  from  loss  of  normal  dentin. 
The  Ungual  wall  at  B  has  been  reduced 
with  a  stone  and  beveled  so  that  it  may  be 
reproduced  with  amalgam.  This  will 
lock  the  cusp  so  that  it  will  not  be  sub- 
ject to  fracture.  The  bucco-axial  Une 
angle  is  shown  at  A.  This  is  part  of  the 
resistance  form  and  is  an  aid  in  preventing 
flow  of  amalgam  from  the  cavity. 


Usually  teeth  in  this  concUtion  are  beHeved 
to  be  impossible  to  restore,  except  with  a 
banded  crown,  but  the  writer  seldom  hesi- 
tates to  restore  such  teeth  vnth.  amalgam. 
Records  of  these  extensive  operations,  cover- 
ing a  period  of  years,  have  yet  to  reveal  the 
first  failure,  either  from  recurrence  of  decay. 


fracture,  or  any  other  cause.  The  outhne 
form  for  such  restorations  is  shown  in  Figure 
5.  The  gingival  walls,  A  and  F,  are  ex- 
tended and  squared  out  as  they  would  be 
for  an  operation  on  either  the  mesial  or  dis- 
tal surface.  As  both  the  buccal  and  lingual 
walls  are  weakened  by  extensive  decay, 
the}'  have  been  reduced  so  that  the  amal- 
gam restoration  will  have  sufficient  strength 
to  withstand  all  the  forces  of  mastication. 

The  outline  form  of  cavities  which  occur 
upon  the  buccal,  lingual,  and  occlusal  sur- 
faces is  identical  with  the  form  which  is 
used  in  ca\dty  preparation  for  gold  foil. 

Adjustment  of  the  Rubber  Dam 

If  the  rubber  dam  has  not  been  adjusted 
at  the  beginning  of  the  operation,  this 
should  be  done,  or  some  other  means  should 
be  provided  to  keep  the  cavitj^  free  from 
moisture,  as  soon  as  the  outline  form  is 
completed.  It  is  not  sufficient  to  prepare 
the  cavit}'  and  then  dn,'  it,  since  in  this 
case  it  will  be  impossible  to  remove  the 
debris  and  the  dried  salts  of  the  sahva  from 
the  ca\dty  and  its  margins.  Xo  moisture 
should  come  in  contact  with  the  cavit}' 
after  the  final  cutting  is  done. 

2  —  Resistance  Form 

The  resistance  form  of  the  cavity  should 
be  the  same  for  amalgam  as  for  gold,  that 
is  the  cavity  should  have  a  flat  gingival 
wall,  ■\\'ith  definite  angles,  and  a  broad,  flat 
step,  or  pulpal  wall.  The  base  of  the  cavit}' 
should  be  at  right  angles  to  the  force  of 
occlusion  and  usually  should  be  at  right 
angles  to  the  long  axis  of  the  tooth.  This 
form  is  illustrated  in  Figure  1  where  the 
ca^dty  sho^Ti  has  a  flat  base  on  the  gingival 
and  pulpal  walls,  with  buccal  and  Ungual 
waUs  at  right  angles  to  the  base  of  the  cavity. 


CAVITY        PREPARATION 


FOR 


AMALGAM 


3  —  Retention  Form 

The  ideal  retentive  form  is  a  box  form, 
that  is  a  fiat  base  witli  walls  at  right  angles 
to  the  base,  as  this  form  gives  the  greatest 
strength  possible  to  the  lateral  walls.  If 
amalgam  is  properly  condensed  into  a 
cavity  of  this  kind,  it  will  be  retained  safely. 
However,  as  such  ideal  cavities  are  not  often 
presented,  we  must  consider  the  conditions 
which  actually  exist. 

As  amalgam  tends  to  flow  under  pressure, 
it  is  permissible,  in  compound  cavities,  to 
use  more  retention  than  is  necessary  for 
gold.  This  is  accomphshed  by  carrying  the 
bucco-axial  and  linguo-axial  line  angles,  in 
a  very  slightly  retentive  form,  to  a  point 
near  the  occlusal  surface.  This  statement 
is  not  intended  to  countenance,  in  any  way, 
deep  or  decided  undercuts  which  may 
weaken  the  walls  and,  subsequently,  permit 
fracture.  These  lines  are  carried  out  soleh^ 
for  the  purpose  of  resisting  the  flow  of 
the  amalgam. 

Both  Figures  2  and  4  show  the  correct 
retention  form  for  the  bucco-axial  hne  angle 
at  A.  A  part  of  the  retention  form  shown  in 
Figure  3  is  a  small  slot,  at  A,  cut  in  the 
lingual  wall  gingivally  to  lock  the  amalgam 
from  any  tendency  to  flow  distally  from  the 
cavity.  At  B  the  wall  has  a  bevel  which, 
when  covered  with  amalgam,  will  overcome 
any  tendency  of  the  wall  to  fracture. 

In  cavities  hke  that  shown  in  Figure  5, 
an  extensive  resistance  surface  for  the 
anchorage  of  the  restoration  is  given  by  the 
flat,  wide,  subpulpal  wall.  This  has  been 
broadened  so  that  only  a  small  amount  of 
dentin  remains  on  either  the  buccal  or 
Ungual  waU.  As  aU  the  force  of  occlusion 
is  applied  to  this  subpulpal  wall,  very 
little  anchorage  is  required.  There  is  a 
shght  undercut  at  the  base  of  the  cavity 


at  C  and  a  bevel  from  D  to  E  which  adds 
strength.  The  cusps  have  been  reduced 
about  two-thirds  of  the  depth  of  the  crown 
to  a  very  safe  and  immune  area.  The 
gingival  form,  when  restored,  is  anatomic- 


Figure  3  represents  a  cavity  in.  the  disto- 
occlusal  surfaces  of  a  left  upper  molar. 
Decay  has  been  very  extensive,  the  pulp 
has  been  removed  from  the  tooth,  and  the 
disto-Ungual  cusp,  being  weakened,  has 
been  reduced  so  that  it  may  be  restored 
with  a  mass  of  amalgam  sufficient  to  give 
ample  strength  for  any  occasion.  At  A 
is  a  small  slot  cut  in  the  lingual  wall 
gingivally  to  lock  the  amalgam  from  any 
tendency  to  flow  distally  from  the  cavity. 
At  B  the  wall  has  a  strong  bevel  which, 
when  covered  with  amalgam,  wiU  over- 
come any  tendency  of  the  waU  to  fractiure. 
The  pulp  chamber,  fiUed  with  cement  to 
the  level  of  the  gingival  wall,  is  shown  at 
C.  Cavities  of  this  class  are  encountered 
very  frequently  in  practice;  when  they 
are  properly  restored  with  amalgam,  the 
result  should  be  permanent. 

aUy  correct  and  remains  free  from  the  irri- 
tation which  must  result  when  a  banded 
restoration  is  used. 

It  is  permissible,  in  pulpless  teeth,  to 
use  the  pulp  chamber  as  an  aid  to  retention, 
as  this  gives  added  strength  and  a  base 


M 


STANDARDIZING         THE         AMALGAM         FILLING 


wliich  is  better,  stronger,  and  more  stable     for  amalgam.    A  study  of  the  enamel  rods, 

than  cement.  as  shown  in  Figures  6  and  7,  will  make  it 

clear  that  a  bevel  to  the  cavo-surface  angle 
4  —  Convenience  Form 

Extension  for  convenience  is  less  essential 
for  amalgam  than  for  gold.  Usualty  when 
the  preceding  forms  of  retention  have  been 


Figure  4  is  an  upper  bicuspid  with  a 
cavity  in  the  mesio-occlusal  surfaces,  in- 
volving the  Ungual  cusp.  As  shown  at  B, 
this  cusp  has  been  reduced  so  that  it  may 
be  restored  with  amalgam.  At  A  the 
bucco-axial  Une  angle  shows  the  correct 
resistance  form  for  amalgam. 


observed,  the  convenience  form  is  sufficient. 
It  should,  however,  be  observed  that  suit- 
able condensing  instruments  will  enter  the 
cavit}'  in  lines  which  will  produce  thorough 
adaptation. 

5  —  Removal  of  Carious  Dentin 

AH  carious  dentin  should  be  removed 
after  completmg  the  outline  form,  to  avoid 
accidents  to  the  pulp. 

6  —  Finish  of  Enamel  WaUs 

It  is  generally  beheved  by  the  profession 
that  enamel  margins  should  not  be  beveled 


Figure  5  shows  an  upper  molar  prepared 
for  an  amalgam  crown.  The  gingival  walls 
are  extended  and  squared  out  as  they 
would  be  for  an  operation  on  either  the 
mesial  or  distal  surface.  As  both  the 
buccal  and  Ungual  waUs  are  weakened 
by  extensive  decay,  they  have  been  so 
reduced  that  the  amalgam  restoration 
wiU  have  sufficient  strength  to  withstand 
all  the  forces  of  mastication.  The  floor 
of  the  pulp  chamber  at  B  is  flat  and  broad- 
ened out  so  that  there  is  only  a  smaU 
amount  of  dentin  left  on  either  the  buccal 
or  Ungual  waUs.  As  aU  the  force  of 
occlusion  is  appUed  to  this  broad  flat 
sub-pulpal  waU,  very  Uttle  anchorage  is 
required.  There  is  a  very  sUght  undercut 
around  the  base  of  the  cavity  at  C,  the 
bevel  from  D  to  E  gives  added  strength. 
Though  such  cavities  as  this  seem  difficult, 
they  are  reaUy  simple  to  prepare  and, 
when  a  matrix  is  properly  adjusted,  they 
are  not  difficult  to  restore. 

on  the  occlusal  surface  is  necessary  in  in- 
stances when  the  margin  approaches  a  cusp 
or  marginal  ridge. 

It  is  of  the  greatest  importance  that  all  of 
the  surface  margins  shall  be  at  such  an  angle 
that  there  are  no  short  unsupported  rods 
of  enamel  at  the  surface.  These  are  hkely 
to  become  dislodged,   after  the  filling  has 


[10] 


CAVITY        PREPARATION        FOR        AMALGAM 


been  placed,  causing  an  uneven  surface  for 
the  lodgment  of  food  solutions  and,  sub- 
sequently, the  failure  of  the  operation.  To 
avoid  this,  the  enamel  should  be  cut  with 
the  long  axis  of  the  rods  in  the  preparation 
of  the  cavity,  and  in  finishing  the  cavo- 
surface  angle  a  sharp  broad  chisel  should 
plane  the  entire  depth  of  the  enamel  at  an 
angle  which  will  insure  the  absence  of  any 
short  rods  at  the  surface. 

Dr.  Black  advocates,  in  the  preparation  of 
the  cavo-surface  angle  for  gold  foil,  a  bevel 
one-fourth  of  the  depth  of  the  enamel.  This 
bevel,  which  is  entirely  proper  for  gold,  but 
would  be  very  unsafe  for  amalgam,  is  shown 


Figure  6  is  a  diagrammatic  representation 
of  the  enamel  rods,  showing  the  direction 
in  which  they  are  placed  in  relation  to  the 
several  surfaces  of  the  tooth.  The  oper- 
ator should  take  advantage  of  a  knowledge 
of  the  direction  of  these  rods  when  cutting 
and  cleaving  the  enamel  for  the  prepara- 
ation  of  cavities  for  amalgam,  especially 
when  forming  the  cavo-surface  angle. 


at  A  in  Figure  7.  The  advantage  in  strength 
to  be  gained  by  the  use  of  the  bevel  shown 
at  C  in  this  illustration,  for  amalgam,  will 
be  seen  at  once. 

Figure  8  shows  the  manner  of  holding  the 
chisel  when  planing  the  enamel  wall.    The 


cavo-surface  angle  is  at  A,  the  dento-enamel 
junction  at  B. 

7  —  Making  the  Cavity  Toilet 

This  represents  the  final  work  upon  the 
cavity  such  as  examining  thoroughly  every 
margin,  surface,  and  angle  with  a  magni- 


Figure  7  —  A  section  of  enamel  through 
wMch  a  cavity  has  been  cut  into  the 
dentin.  At  A  a  short  bevel,  one-fourth 
of  the  depth  of  the  enamel,  is  shown. 
This  is  a  bevel  advocated  by  Dr.  Black 
in  cavity  preparation  for  gold  foil.  The 
correct  bevel  for  amalgam,  where  the 
occlusion  is  a  strain  to  the  material,  is 
shown  at  C.  The  thin  margin  of  material 
which  is  formed  when  the  bevel  A  is  used, 
is  shown  at  B.  A  comparison  of  the  bulk 
of  amalgam  at  D  will  show  the  added 
strength  gained  by  the  change  in  angle. 
This  illustration  is  adapted  from  a  famihar 
one  in  Black's  "Operative  Dentistry." 


fying  glass  of  low  power  and  wiping  or 
sweeping  all  of  the  cavity  surfaces  with 
cotton  or  spunk  to  remove  fine  particles  of 
tooth  debris  which  can  not  be  removed  in 
other  ways. 

Summary  of  Cavity  Preparation  for 
Amalgam 

Proper  cavity  preparation  for  amalgam  is 
identical  with  Dr.  Black's   cavity  prepara- 


[11] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


tion  for  gold  foil,  with  slight  modifications. 

as  noted. 

Outline  Fonn:  As  for  gold 

Modificatioti:  Broad  outline  where  occlusal 
and  proximal  portions  of  the  cavity  join. 

Resistance  Form:  As  for  gold 

Retetition  Form:  As  for  gold 

Modification:  Angles  slightly  more  reten- 
tive inform. 

Convenience  Form:  Not  so  necessaiy  as  for 
gold 

Modification:    Should    allow    condensing 
instruments,  suitable  for  amalgam,  to  enter. 

Removal  of  Carious  Dentin:  As  for  gold 

Finish  of  Enamel  Walls: 

Modification:  Bevel  entire  depth  of  enamel 
instead  of  one-fourth. 

Cavity  Toilet:  As  for  gold 

Modification:  Supply  iriissing  walls  with 
matri.v. 


Figure  8  shows  a  cavity  preparation  for 
amalgam  in  an  upper  molar,  also  the  posi- 
tion in  vrhich  the  chisel  should  be  held 
when  planing  the  enamel  to  obtain  the 
proper  bevel  for  amalgam.  The  cavo- 
stirface  angle  is  at  A,  the  dento-enamel 
junction  at  B. 


Cement  Lining  for  Amalgam 

Many  operators  advocate  a  thin  lining  of 
cement  for  the  walls  of  a  cavity  about  to  be 
filled  with  amalgam,  claiming  an  advantage 
in  that  the  cement  will  act  as  a  seal  between 
the  amalgam  and  the  tooth  structure.  With 
certain  classes  of  amalgam,  this  is  probably 
an  advantage;  however  it  has  certain  dis- 
advantages. Cement  in  the  thin  consistency 
necessaiy  to  its  use  in  this  mamier  is  neither 
strong  nor  impervious,  it  is  Uable  to  re- 
crystallization  and  when  this  occurs  mois- 
ture will  be  absorbed  at  the  margins  of  the 
ca\'ity  and  discoloration  and  future  trouble 
will  result. 

With  the  accurately  balanced  dental 
amalgam  alloys,  correctly  manipulated,  it 
is  our  experience  that  a  more  permanent 
result  is  obtained  without  the  cement  in- 
termediary. An  amalgam  which  does  not 
move  from  the  cavity  wall  will  exclude 
moisture  and  the  bacteria  of  deca^-  suffi- 
ciently to  prevent  recurrence  of  caries.  In 
addition  to  this,  amalgam  in  contact  with 
the  tooth  substance,  either  by  exerting  an 
antiseptic  action,  or  bj'  some  means  of 
wliich  we  have  no  formulated  knowledge  at 
the  present  tune,  exerts  a  decided  inhibitory 
action  against  the  bacteria  of  caries.  We 
do  know  that  some  of  the  metals  contained 
in  amalgam  have  a  decided  inliibitoiy 
action  against  the  growth  of  bacteria  and 
that  their  salts  are  among  the  most  effective 
antiseptics  and  disinfectants. 

A  further  disadvantage  of  the  cement 
lining,  when  used  in  thin  consistency  with 
amalgam  condensed  against  it,  is  that  it 
obliterates  the  definite  form  of  the  ca\'ity 
preparation  and  especially  tends  to  fill  all 
angles  and  line  angles  so  that  the  amalgam 
does  not  have  the  definite  form  which  we 
anticipated  in  the  preparation  of  the  cavity. 
When  it  is  desirable  to  use  cement,  either 


[12] 


MATRICES         FOR         AMALGAM         RESTORATIONS 


as  a  base  in  the  pulp  chamber,  or  as  a  lining 
for  the  cavity  walls,  a  cement  of  the  greatest 
density  should  be  chosen  and,  after  intro- 
ducing, should  be  permitted  to  harden  for 
several  hours  in  order  that  the  bulk  changes, 
which  always  occur  with  the  oxy phosphates, 
may  fully  take  place  before  the  amalgam  is 
introduced.  After  the  cement  has  thor- 
oughly hardened,  the  cavity  preparation 
should  be  completed,  as  previously  de- 
scribed, considering  the  cement  as  tooth 
structure  and  a  part  of  the  walls  of  the  tooth. 

To  Prevent  Thermal  Shock 

When  it  is  desired  to  prevent  thermal 
shock  to  the  pulp,  a  thin  solution  of  resin 
in  chloroform  may  be  used  with  approxi- 
mately the  same  advantage  as  cement. 
This  will  not  obhterate  the  cavity  lines, 
neither  is  it  soluble  in  moisture,  and  it  will 
neither  shrink  nor  expand.  If  the  cavity 
is  well  dried,  it  will  seal  the  open  tubuU. 

Matrices  for  Amalgam 

In  all  classes  of  cavities  where  one  of  the 
walls  of  the  tooth  is  missing,  it  is  of  first 
importance  that  some  form  of  matrix  should 
be  used  to  assist  in  forming  the  lost  contour 
of  the  tooth  and  to  aid  in  conforming  the 
amalgam  to  the  cavity. 

The  placing  of  matrices  requires  ingenuity 
and  careful  workmanship.  An  effective 
matrix  must  be  of  such  form  that  it  can  be 
adapted  closely  to  the  gingival  margin,  but 
it  should  not  be  adjusted  so  closely  that  the 
amalgam  can  not  be  adapted  completely; 
it  must  have  such  rigidity  of  wall  that  it 
will  not  be  forced  out  of  position,  allowing 
the  amalgam  to  "landslide"  from  the  cavity 
and  fail  to  be  condensed  well  at  the  margins; 
it  must  be  arranged  so  that  contact  with 
the  approximating  tooth  may  be  obtained, 
without  loss  of  space;  it  must  be  one  which 


can  be  removed  in  a  short  space  of  time, 
without  distorting  the  filhng. 

The  matrix  which  most  nearly  meets  all 
these  requirements  is  the  tied  copper  matrix, 
made  from  36  gauge  sheet  copper. 

MAKING  THE  TIED  COPPER  MATRIX 
To  make  the  copper  pUable  it  should  be 
annealed  by  heating  it  in  the  flame  and  dip- 


Figure  9  shows  the  steps  in  the  prepara- 
tion of  the  tied  copper  matrix.  A  strip  of 
metal  cut  to  suitable  size  with  hole  for 
contact  point  cut  out  with  the  rubber 
dam  punch  is  shown  at  A.  At  B  button- 
hole scissors  are  cutting  occlusally  and 
gingivally  from  the  contact  point  to  weaken 
the  matrix  so  that  it  can  be  removed 
easily.  C  is  the  completed  matrix.  Two 
forms  of  ears  are  shown  at  D  and  E. 
Either  may  be  used  to  hold  the  ligature 
in  place. 

ping  it  in  water,  alternately,  two  or  three 
times.  A  strip  of  the  annealed  metal,  long 
enough  to  pass  sufficiently  about  the  tooth, 
should  be  cut  as  shown  in  Figure  9;  it  does 
not  need  to  encircle  the  tooth  entirely,  but 
should  extend  past  the  margins  of  the  cavity 
as  far  as  it  may  without  inconvenience.  In 
width  it  should  extend  somewhat  beyond 
the  length  of  the  tooth  occlusally,  to  give 
the  matrix  additional  rigidity. 

THE  CONTACT  POINT 

With  the  band  in  position  on  the  tooth, 
observe  and  mark  the  correct  point  for  the 
contact  with  any  sharp  cutting  instrument, 
as  shown  in  Figure  10.  With  the  rubber 
dam  punch  make  a  small  hole  where  the 


[13] 


STANDARDIZING         THE         AMALGAM         FILLING 


contact  should  come,  as  shown  at  A,  Figure 
9,  then  with  buttonhole  scissors,  or  a  sharp 
instrument,  cut  the  metal  occlusally  and 
gingivall.v  from  the  hole  to  weaken  the 
matrix  so  that  it  may  be  more  easily  torn 
in  two  when  removing  it. 

Occlusally  the  slit  should  be  cut  to  or 
past  the  occlusal  surface  so  that  an  instru- 


Figure    10  —  Marking    the    position    for 
contact  point  with  a  sharp  instrument. 

ment  may  be  hooked  into  it  and  used  to 
cut  the  band  to  the  occlusal  margin  before 
it  is  removed.  With  pliers  turn  up  little 
ears  at  the  gingival  angles,  to  engage  the 
ligature,  and  the  matrix  is  ready  to  be 
placed  upon  the  tooth  and  tied.  Two  forms 
of  ears  for  the  attachment  of  ligatures  are 
shown  at  D  and  E,  Figure  9,  and  the  posi- 
tion of  the  scissors  in  cutting  slits  from  the 
contact  point  is  shown  at  B. 

LIGATING  THE  MATRIX 

Place  a  ligature  once  around  the  tooth 

and  matrix  and  make  a  single  knot,   as 

shown  in  Figure  11,  then  pass  one  end  of 

the  ligature   around   the  tooth   again,   so 


that  the  ligature  surrounds  the  tooth  twice 
with  only  a  single  tie.  Now  the  ligature 
should  be  held  taut  with  one  hand  while, 
with  an  instrument,  it  is  adjusted  about 
the  tooth  and  matrix  and  carried  above 
the  gingival  margin,  as  shown  in  Figure 
12.  If  the  opening  for  the  contact  is  not 
in  the  proper  place,  it  may  be  adjusted  by 
drawing  either  end  of  the  ligature.  Now 
tie  the  ligature  with  a  surgeon's  knot  and 
continue  to  wrap  it  about  the  tooth  mesially 
and  distally,  until  the  form  of  the  inter- 
proximal space  is  produced  as  desired,  tying 
finally  on  the  buccal,  as  shown  in  Figure  13. 
After  the  first  tie,  avoid  making  the  matrix 
too  tight;  leave  it  so  that  some  of  the 
amalgam  will  be  forced  over  the  margins 


Figure  11  shows  the  matrix,  with  hole  for 
contact  and  slits  to  weaken  it  for  removal, 
in  position  upon  the  tooth;  also  the  first 
tie  of  the  ligature. 

as  it  will  be  found  almost  impossible  to 
carry  amalgam  perfectly  to  the  margins  un- 
less some  of  it  is  allowed  to  pass  over  them. 
If  the  outline  of  the  cavity  is  extensive 
and  involves,  to  any  extent,  the  buccal 
and  lingual   walls,   the  matrix  should   be 


[14] 


MATRICES        FOR        AMALGAM        RESTORATIONS 


burnished  to  position  and  a  roll  of  softened 
modeling  compound  should  be  pressed 
against  it  and  extended  mesially  and  dis- 
tally  against  the  other  teeth.  This,  when 
hard,  is  easily  held  in  position  and  will 
support  the  matrix  against  the  force  of 
heavy  condensing. 

As  the  amalgam  is  condensed,  it  will  pass 
through  the  hole  punched  in  the  matrix 
and  will  be  forced  against  the  proximal 
surface  of  the  adjacent  tooth  at  the 
position  desired  for  contact.     Heavy  pres- 


Figure  12  —  Holding  both  ends  of  the 
Ugature  with  one  hand,  while  the  matrix 
is  adapted  about  the  gingival  margin  with 
an  instrument. 


sure  on  the  amalgam,  driving  it  through 
this  opening  in  the  matrix,  will  produce 
a  certain  amount  of  separation  of  the 
teeth.  If  more  separation  is  desired,  a 
separator  should  be  placed  between  the 
teeth,  over  the  matrix,  in  such  a  position 
that  it  will  not  impinge  upon  the  margins 
of  the  cavity  at  any  point  and  so  prevent 
perfect  adaptation  of  the  amalgam. 


This  form  of  matrix  has  several  advan- 
tages; it  can  be  quickly  and  accurately 
applied  and  is  very  readily  adapted  to  the 


Figure  13  - 
to  position. 


The  completed  matrix  ligated 


peculiarities  of  the  case  in  hand;  in  cases 
where  separation  is  desired  a  separator  can 
be  placed  over  it  and  will  adhere  to  the 


Figure  14  —  Drilling  a  hole  for  the  point 
of  contact  with  a  small  round  bur,  from 
the  inside  of  the  seamless  matrix  band. 


tooth;  there  is  no  space  lost  for  thickness 
of  the  metal;  it  is  easily  removed  without 
disturbing  the  filling. 


[15] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


THE  SEAMLESS  BAND  COPPER  MATRIX 

When  a  complete  amalgam  restoration, 
or  amalgam  crown,  is  indicated,  the  seam- 
less band  copper  matrix  may  be  used  to 
advantage    and   can   usually   be   adapted 


metal  immediately  around  these  points 
should  be  thinned  and  made  to  assume 
a  concave  form  by  grinding  with  a  small 
round  stone.  This  will  produce  a  better 
mold  for  the  approximating  surface  of  the 


Figures  15,  16  and  17  show  various  methods  of  slitting  the  matrix  bands.  Figures  15  and  17  show  bands 
slit  from  the  gingival  through  and  slightly  beyond  the  contact  point.  At  B,  Figure  17,  the  band  is  lapped  to 
conform  more  closely  to  the  tooth.  Figure  16  shows  bands  slit  both  occlusally  and  gingivally  from  the 
contact  point,  without  cutting  to  either  margin.  Small  ears  turned  up  to  engage  the  ligature  are  shown  at 
C,  in  each  illustration. 


quickly  and  conveniently.  A  band  which 
will  fit  the  tooth  to  be  restored,  as  nearly 
as  possible,  is  chosen  and  is  trimmed  and 
festooned  to  the  gingival  outline.  The 
points  of  contact  are  marked  with  any  con- 
venient cutting  instrument,  in  the  same 
manner  as  for  the  tied  matrix  shown  in 
Figure  10,  and  the 
band  is  then  re- 
moved from  the 
tooth  and  placed 
upon  a  block  of  soft 
wood  while  a  small 
round  bur,  Xo.  2, 
is  used  to  drill  holes 
in  it  at  the  points  of 
contact,  as  shown 
in  Figure  1-i.  The 
entire  head  of  the 
bur  should  be  al- 
lowed to  pass 
through  the  band 
at  the  contact 
points    and    the 


Figure  18  —  The  first  tie  of  the  Ugature 
about  the  matrix  band  is  shown  here. 
The  blunt  instrument  used  for  holding 
the  Ugature  is  also  used  for  adapting  the 
matrix  about  the  gingival  margin. 


tooth  and  when  amalgam  is  condensed 
within  the  matrix,  it  will  assume  the  form 
of  this  mold  and,  passing  through  the 
hole  at  the  contact  point,  will  form  a 
smooth,  rounded,  normal  contacting  sur- 
face at  the  desired  point. 

CLIPPING  THE  BANDS 

Figure  15  shows 
the  band  after  the 
contact  hole  has 
been  cut  and  the 
band  has  been  slit 
from  the  gingival 
edge  at  A  through 
and  slightly  be- 
yond the  contact 
opening.  This  slit- 
ting of  the  band 
allows  it  to  be 
lapped,  when  this 
is  desirable,  as 
shown  at  B,  Figure 
17,  so  that  it  will 
conform    more 


[16] 


MATRICES         FOR        AMALGAM         RESTORATIONS 


closely  to  the  tooth  when  it  is  tied  in 
place,  and  also  allows  the  band  to 
be  removed  easily,  by  tearing,  after  the 
amalgam  has  hardened.  Various  methods 
of  clipping  the  bands  may  be  used  as  con- 
ditions and  the  forms  of  the  teeth  vary. 
It  is  often  advisable  to  slit  the  band  from 
the  occlusal  surface  through  the  contact 
opening,  or  it  may  be  slit  both  occlusally 
and  gingivally  from  the  contact  opening, 
not  cutting  to  either  margin,  as  shown  in 
Figure  16.  Small  ears,  turned  up  for  the 
purpose  of  engaging  the  ligatures  which 
hold  the  bands  in  place  are  shown  at  C 
in  Figures  15,  16  and  17. 

PLACING  THE  SEAMLESS  BAND  MATRIX 

The  seamless  band  copper  matrix  may 
frequently  be  used  without  the  ligature; 


when  it  is  desired  to  use  the  ligature,  how- 
ever, it  should  be  adjusted  about  the 
tooth  in  the  same  manner  as  for  the  tied 
copper  matrices,  previously  described.  Fig- 
ure 18  shows  the  first  tie  of  the  ligature, 
a  single  tie  with  a  double  loop  about  the 
band;  this  illustration  also  shows  the 
method  of  adapting  the  matrix  about  the 
gingival  margin  with  a  blunt  instrument. 

It  will  be  noticed  that  the  bands,  as 
shown  in  Figures  18  and  19,  are  longer 
occlusally  than  the  restoration  will  be 
when  finished.  This  allows  the  amalgam 
to  be  condensed  in  excess,  producing  great 
density  at  the  occlusal  surface. 

Both  the  tied  copper  matrix,  for  partial 
amalgam  restorations,  and  the  seamless 
band  matrix,  for  complete  amalgam  resto- 
rations, are  shown  in  Figure  19. 


Figure  19  shows  two  forms  of  copper 
matrices  in  position  on  the  teeth.  At  A  a 
matrix  which  does  not  entirely  encircle 
the  tooth  is  shown  in  position  upon  an 
upper  second  bicuspid.  At  C  an  opening 
is  punched  in  the  matrix  at  the  point  where 
the  filUng  should  contact  with  the  distal 
surface  of  the  first  bicuspid.  To  permit 
the  matrix  to  be  torn  away  more  easily 
after  the  amalgam  is  condensed,  the 
matrix  is  slit  both  gingivally  and  occlu- 
sally from  the  opening  C. 

A  seamless  band  copper  matrix,  used  in 
the  construction  of  amalgam  crown  res- 
torations, is  shown  at  B.  The  point  for 
contact  with  the  first  molar  is  shown  at  D, 
a  similar  provision  is  made  for  contact 
with  the  third  molar. 

After  amalgam  has  been  condensed  in 
such  matrices,  it  should  be  carved  until 
the  occlusion  is  correct  and  the  natural 
tooth  form  is  restored.  If  the  matrix 
should  interfere  with  the  occlusion  it  may 
be  ground  away  until  the  occlusion  is 
correct.  It  is  usually  best  to  leave  such 
a  matrix  in  position  for  a  few  hours  at 
least,  as  such  large  restorations  must  be 
handled  carefully  until  the  amalgam  is 
very  hard,  otherwise  the  entire  restora- 
tion may  be  broken  off  at  the  point  of 
anchorage.  The  ligatures  which  hold  the 
matrices  in  position  are  at  E  and  F. 


[17] 


STANDARDIZING         THE         AMALGAM         FILLING 


Section  II.     Dental  Amalgam  Alloys 


THE  second  essential  for  standardized 
amalgam  technic  is  the  selection  of  the 
best  alloy  that  it  is  possible  to  obtain  for 
the  amalgam.  The  question,  "How  are 
we  to  know  the  best  alloy  to  use?",  is 
asked  of  the  writer  more  frequently  than 
any  other.  The  answer  to  this  question 
will  be  found  by  considering  those  qualities 
of  an  alloy  which  are  essential  to  permanent 
results  when  the  allo}'  is  amalgamated  and 
used  for  the  restoration  of  carious  teeth. 
Practical  experience  has  led  to  the  con- 
clusion that  a  dental  amalgam  alloy  must 
satisfy  the  following  requirements: 

1 .  It  must  amalgamate  in  such  a  manner 
that  it  will  be  capable  of  accurate  manipu- 
lation by  dentists  who  are  familiar  with 
restoration  technic. 

2.  It  must  possess  inherent  structural 
strength  and  impart  this  quahty  to  the 
resulting  amalgam.  Its  amalgam  must  be 
sufficiently  strong  to  withstand  the  con- 
tinued force  of  mastication;  it  must  not 
flow  from  the  cavit}^  under  this  stress; 
its  margins  must  endure  this  force  without 
fracture. 

3.  It  must  be  chemically  and  electro- 
chemically  resistant  to  deterioration  by 
tarnishing  or  corrosion. 

4.  It  must  be  of  the  type  known  as 
balanced  aUoy,  that  is,  when  properly 
amalgamated  and  condensed  in  the  cavity, 
the  amalgam  must  remain  tight  to  the 
cavity  walls,  it  must  not  contract,  and 
must  have  a  minimum  and  regulated 
amount  of  expansion. 

5.  It  must  conform  to  metaUographic 
principles. 

6.  It  must  require  the  minimum  amount 
of  mercury. 

7.  Its  color  should  be  pleasing. 


8.  It  must  not  contain  materials  which 
will  injure  the  tissues  or  discolor  them. 

It  is  not  an  easy  matter  to  incorporate 
all  of  these  quahties  in  one  alloy,  but  it  is 
possible  and  we  should  not  be  satisfied 
with  an  alloy  which  fails,  in  even  one 
particular  to  meet  these  requirements. 

A  careful  study  of  the  physical  and 
chemical  properties  of  the  various  metals 
which  have  been  used  for  dental  alloys 
permits  us  to  predicate  the  probable 
qualities  which  the  metal  will  confer  upon 
the  alloy  and,  together  with  a  consider- 
ation of  methods  which  have  been  used 
for  combining  the  alloy  metals,  should  be 
helpful  in  choosing  the  best  alloy. 

Dental  Amalgam  Alloy  Metals 

Although  experiments  with  other  metals 
have  been  made  none  seem  to  have  been 
found  which  have  added  sufficient  desir- 
able quahties  and  the  only  metals  which 
have  been  used  to  anj-  extent  for  dental 
amalgam  alloys  are  silver,  tin,  copper, 
gold,  and  zinc.  A  tabulated  comparison 
of  important  physical  and  chemical  charac- 
teristics of  these  metals  will  be  found  on 
the  succeeding  page.  Some  characteristics 
which  especially  affect  their  use  in  dental 
amalgam  alloys  are  noted  as  follows: 

SILVER 

Silver  occludes  twenty-two  volumes  of 
oxygen,  when  molten,  which  it  gives  off 
with  great  vigor  upon  sohdification.  In 
order  to  avoid  undesirable  oxides  and 
resulting  eutectics,  from  this  cause,  it 
should  be  melted  in  the  electric  furnace, 
under  hydrogen. 

Silver  increases  in  volume  when  amalga- 
mated, can  not  be  easily  manipulated,  and 
is  subject  to  sulphide  blackening.  In 
dental    amalgam    alloys    it    lessens    flow, 


[18] 


PHYSICAL         PROPERTIES         OF         ALLOY         METALS 


o 

O  CO 
O   CO 

o  ^ 


t^  o 

CO   i-H 

CO 


(M   CO 


1>  o 


o  o 

<M   O 

05  d 


02 


o  o 


O    OJ 


O  CO 
(M   O 

d  d 


CO 

CO 
O    05 

i>^  d 


CO   LO 
CO  o 


>  K 

O    Of 


.2  ^ 


9   fl 


W 


[19] 


o  o 

CO 

o 


o  o 

o 
o 


o 
o 
J> 

o  d 

o 

CO 


o  o 

o 

CO 


o  d 

CO 


>     >: 
O    > 

O  T3 
O    S3 

.g5 

WW 


00  t^ 

CO   lO 
I     CO 


05    GO 


(M  O 

CO   CO 
O  lO 

.-H     C-l 


o   o 

O    o3 


'^  o 

00  ^ 

O  CO 

--I  (M 


(M   O 
CO  t^ 


CO  lO 
05    05 


o 


o 


Ph 


.1:3   c 


.2  S 

o  a> 

HJ  P-l 

-^J  O 


0^  1i 

•-H    hC 

-^  -r 

^« 

o 

-ij 

^ 

.b  ^ 

«  I- 

3     --H 

03     O 

^    oi 

f^  hJ 

pq  P^ 

^ 

bC 

M 

^§ 

>>-^ 

o  -^ 

t-(    bC 

^  1  '*"■ 

QJ  .-, 

O      !- 

>w 

>^pq 

-tj 

bJD  faC 

WW 


P^ 


y^  pq 


P5  pq 


^ 

>. 

x> 

-fj 

a 

;J2 

<u 

•+J 

03 

3 

Sq 


O  Ph 


^    O 


o 

-(-= 

n 

a; 

-fj 

o 

a 

3 

'a; 

o 

C3 

o 

S-H 

Xi 

1-^    o3 


^  t3    03 
^    «1^    t^ 

i-^  'S  "w 


c3 


OJ 


0)     ^    o3 
^    cc    o  (72 


CD     O 
?-(     ^ 

>5  O 
>5 


H 


O 

C 

o 

bC 

c 
o 


o 

CO 


c3 


sj   d 

5       <B 


Q 


<D      O) 

.—I     a> 

>»,  O 


w 


STANDARDIZING         THE         AMALGAM         FILLING 


hastens  hardening,  forms  the  primar\^ 
freezing  network  upon  which  amalgam 
largely  depends  for  strength,  and  adds 
other  desirable  qualities  which  may  be 
deduced  from  its  characteristics  as  indi- 
cated in  the  table  of  physical  properties. 

A  homogeneous  silver  amalgam  can  not 
be  made  by  triturating  silver  filings  with 
mercury,  since  these  merely  envelope, 
that  is,  each  grain  becomes  coated  with 
amalgam,  resisting  establishment  of  equi- 
librium, even  when  heated  moderately. 
Uniform  silver  amalgam  is  produced  at  the 
boiling  point  of  mercury,  357°  C. 

Bomb  Amalgam 

To  determine  the  structural  constituents 
actually  present  in  silver  amalgams,  a 
constitutional  study  of  the  series  was  made 
by  preparing  amalgam  in  the  bombs  shown 
in  Figure  20.  Weighed  portions  of  silver 
and  mercury  were  placed  in  the  bomb,  the 


Figure  20  —  Steel  bombs  used  to  contain 
alloy  and  mercury,  when  amalgamated  by 
heating  to  the  boiling  point  of  mercury. 

screw  plug  was  inserted,  and  the  whole 
was  heated  in  the  electric  furnace  for  a 
suitable  period  of  time,  at  temperatures 
ranging  near  the  boiling  point  of  mercury. 
Naturally  the  time  and  temperature  neces- 
sary for  thorough  amalgamation  increase 
with  the  increase  in  the  percentage  of 
silver. 

Figure   21    is   a   photomicrograph   of   a 
bomb  amalgam  containing  43  per  cent  of 


mercury;  this  shows  large  masses  of 
primary-freezing  silver-rich  solid  solution 
embedded  in  the  darker,  softer  mercury- 
rich  solid  solution.  Up  to  the  percentage 
of  mercury  established  as  correct  for  dental 
practice,  the  silver  amalgams  are  solid 
solutions  of  considerable  strength  and 
toughness,  but  the  consistency  of  amalgams 
containing  the  percentage  of  mercury 
found  in  the  so-called  Arbor  Dianae 
(AggHg^)  reminds  one  of  lumps  of  moist 
table  salt.  This  hardens  slowly  when 
exposed  to  the  air,  supposedly  due  to  the 
loss  of  mercury  bj^  volatilization,  since  the 
vapor  tension  of  the  latter  is  relatively 
high.  Our  research  indicates  that  what  has 
hitherto  been  considered  the  fundamental 
reaction  of  amalgamation:  Ag,Sn+4Hg  = 
AggHg^+Sn,  rests  on  slight  foundation  and 
does  not  concern  dental  amalgams. 

Neither  "affinity"  nor  "absorption"  de- 
scribes amalgamation.  Silver-mercury  al- 
loys of  any  desired  percentage  of  mercury 
may  be  prepared  readily  and,  in  the  dental 
range,  only  solid  solutions  appear.  A 
recent  publication  states  "When  silver 
is  amalgamated  alone  it  does  not  harden 
to  any  extent,  nor  does  it  disintegrate 
readily."  This  statement  stands  unsup- 
ported by  data  and  actual  research  shows 
that  silver  amalgam  may  be  as  hard  and 
tough  as  brass  when  silver-rich  or  decid- 
edly different  when  mercury-rich.  "Crepi- 
tation" is  due  neither  to  silver  nor  tin 
amalgam,  but  to  the  cold  working  of 
primar}^  freezing  crystalhne  grains  of  the 
dental  amalgam. 

TIN 

Tin  forms  a  very  mobile  fluid,  when 
molten,  having  low  chemical  affinities  thus, 
in  some  respects,  approaching  the  precious 
metals  in  its  chemical  behavior.  It  forms 
a  series  of  solid  solutions,  when  amalga- 


20 


EFFECT 


O   F 


ZINC 


O    N 


AMALGAM 


ALLOYS 


mated,  with  decrease  in  volume.  In  dental 
amalgam  alloys  it  retards  setting,  decreases 
edge  strength,  increases  flow  and  produces 
an  easily  worked  mass.  It  imparts  to  the 
alloy  its  property  of  solubility,  making 
possible  the  more  ready  amalgamation  of 
the  copper  and  silver. 

Tin   readily   dissolves   in   mercury,    the 
solid  solutions  rich  in  tin  being  reasonably 


Figure  21  is  a  photomicrograph  of  a  bomb 
amalgam  of  silver  and  mercury,  contain- 
ing 43  per  cent  of  mercury. 

hard  and  tough,  but  rapidly  losing  their 
desirable  industrial  qualities  with  increase 
in  the  mercury  content. 

COPPER 
Like  silver,  copper  readily  forms  solid 
solutions  with  mercury,  near  357°  C,  amal- 
gamation being  correspondingly  more  dif- 
ficult at  ordinary  temperatures  and  in  the 
copper-rich  portion  of  the  series.  The 
amalgam  will  stand  a  considerable  degree 
of  heat  without  suffering  loss  of  mercury 
through  volatilization.  Copper  is  an 
element  of  strength  in  dental  amalgam 
alloys,  decreases  flow  in  the  amalgam,  and 
possesses  a  desirable  coefficient  with  respect 
to  change  of  volume  upon  amalgamation. 


GOLD 

Gold  makes  amalgam  springy  and  dif- 
ficult to  pack.  It  has  low  tensile  strength, 
is  liable  to  flow,  and  has  a  rather  high 
electric  potential. 

ZINC 

Although  the  use  of  zinc  in  dental 
amalgam  alloys  has  long  been  condemned 
by  those  who  speak  with  authority  in  the 
dental  profession,  its  use  is  still  continued 
and  defended  by  manufacturers  of  alloys, 
and  it  seems  well,  for  this  reason,  to  take 
up  in  some  detail  the  physical  and  chemical 
characteristics  of  this  metal  which  may 
affect  the  alloy,  the  amalgam  which  is 
made  from  it,  and  the  general  health  and 
welfare  of  the  patient  for  whom  the 
amalgam  is  used. 

Volatilization  and  Oxidation 

Reference  to  the  table  of  physical  prop- 
erties shows  that  the  boiling  point  of 
zinc  is  below  the  melting  point  of  silver  and 
copper.  Unless  the  metals  are  alloyed  at  a 
temperature  below  the  boiling  point  of 
zinc,  this  will  cause  a  volatilization  error 
as  an  undetermined  percentage  of  zinc 
will  burn  out  or  distil.  This  error  is  suffi- 
cient to  destroy  the  balance  of  metals 
which  are  placed  in  the  crucible  in  correct 
proportions  and  is  further  increased  by 
the  rapid  oxidation  of  zinc,  when  molten, 
even  at  low  temperatures. 

Dr.  Black:  "Zinc  is  Inadmissible" 

As  Dr.  Black's  research  has  recently  been 
construed  to  favor  the  use  of  zinc  in  dental 
amalgam  alloys,  it  seems  well  to  quote  here 
his  conclusion  on  this  subject  as  published 
in  "Operative  Dentistry,"  Volume  II, 
page  312,  where  he  states: 

"Experiment  in  watching  fillings  for  five 
years  shows  also  that  one-half  of  one  per 


[21] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


cent  of  zinc  is  inatlniissible  for  the  reason 
that  the  amalgam  will  continue  to  change 
bulk  very  slowly  for  that  time  and  perhaps 
much  longer.  Though  this  change  is  not 
large  (not  more  than  one  to  one  and  one- 
half  points  per  year,  with  one  per  cent  of 
zinc),  it  will  finally  destroy  the  usefulness 
of  the  filling.  This  effect  is  so  subtle  that 
it  was  not  at  first  discovered." 

Dr.  McCauley:  "100  Points  Expansion" 
In  a  paper  entitled  "Amalgams:  Their 
Manufacture,  Manipulation  and  Physical 
Properties,"  read  before  the  National 
Dental  Association,  July  25,  1911,  and 
published  in  "Dental  Cosmos,"  February, 
1912,  Dr.  C.  M.  McCauley  says: 

"Zinc  is  very  unfavorable  in  its  action 
upon  other  metals  in  a  dental  alloy.  I 
made  two  fillings  containing  only  one  per 
cent  of  zinc.  They  behaved  very  well 
under  the  ten  days  test  at  first,  but 
measurements  made  three  months  later 
showed  nearly  100  points  expansion." 

Adhesiveness 
For  the  first  time  in  the  annals  of  metallog- 
raphy,   the    quality    of    adhesiveness    or 
stickiness  has  recently  been  attributed  to 
a  metal.      It  has  been  stated,  erroneously, 


that  zinc  adds  this  quality  to  dental  amal- 
gams. No  recognized  authorities  are 
quoted  in  support  of  this  theory. 

For  one  substance  to  adhere  to  another, 
it  is  necessary  for  one  to  moisten  or  wet 
the  surface  of  the  other,  to  have  gummy  or 
viscous  quality.  Amalgam  might  be  de- 
scribed as  cohesive,  while  in  the  plastic 
state,  in  the  same  manner  that  gold  foil 
is  cohesive,  but  it  has  no  quality  of  sticking 
to  or  adhering  to  tooth  substance.  Zinc 
does  not  cause  amalgam  to  adhere  to  the 
walls  of  the  cavity  or  its  margins;  on  the 
contrary,  its  tendency  to  produce  flow  and 
change  of  form  causes  the  amalgam  to 
draw  away  from  the  margins  and  walls  of 
the  cavity.  Moisture  proof  fillings  are 
obtained  by  condensing  a  balanced  alloy, 
properly  amalgamated,  so  tight  to  the 
cavity  walls  that  penetration  of  the  oral 
fluids  is  prevented. 

Toughness 

It  has  also  been  claimed  that  zinc 
toughens  amalgam  by  raising  the  breaking 
point.  Reference  to  the  table  of  physical 
properties  shows  that  zinc  has  the  lowest 
tensile  strength  of  any  of  the  metals  used 
for  dental  amalgam  alloys. 


A  Comparison  of  the  Electrolytic  Single  Potential  Diflferences  for  a  Zinc  Alloy 
Amalgam  with  Those  for  a  Non-Zinc  Alloy  Amalgam 

Zinc  Alloy  Amalgam  Non-Zinc  Alloy  Amalgam 

Positive  Negative      Positive  Negative 

VOLTS  VOLTS 

Zinc     +.493 


Copper 

—  .607 

Tin 

—  .083 

Silver 

—1.075 

Mercury 

—1.027 

Copper 

—  .607 

Tin 

—  .083 

Silver 

—1.075 

Mercury 

—1.027 

Addition  of  Single  Potentials  Gives  the  Total  Voltage  Between  Any  Pair  of 
Positive  and  Negative  Elements 

Example:    The  voltage  between  zinc  and   copper   is    .493V.   plus   .607V.    equals    I.IOV. 
The   production   of   electrical   energy  in   a   zinc-copper    cell    is    accompanied    by    the 
consumption  of  zinc. 


[22] 


EFFECT 


O   F 


ZINC 


O    N 


AMALGAM 


ALLOYS 


A  series  of  tests  made  by  Dr.  H.  A. 
Merchant  to  determine  the  strength  of 
amalgams,  under  different  methods  of 
manipulation  and  varying  conditions,  has 
a  direct  bearing  on  this  subject.  The 
tabulated  results  of  these  tests  will  be 
found  on  page  46.  Test  No.  1  made  with 
a  non-zinc  alloy,  containing  5  per  cent  of 
copper,  amalgamated  according  to  direc- 
tions, showed  a  crushing  strength  averag- 
ing (for  sixteen  specimens)  437.5  pounds. 
Test  No.  6,  made  with  a  zinc  alloy,  con- 
taining 5  per  cent  of  copper,  amalgamated 
according  to  directions,  showed  a  crushing 
strength  averaging  (for  sixteen  specimens) 
352.5  pounds.  After  heat  treatment  of 
thirtj^-five  minutes  at  150°  F.,  approximat- 
ing the  effect  of  hot  drinks  and  food,  the 
non-zinc  alloy  amalgam  showed  a  loss  of 
strength  of  50  pounds,  while  the  zinc  alloy 
amalgam  lost  150  pounds,  leaving  a  net 
crushing  strength  of  only  202.5  pounds, 
compared  with  387.5  pounds  for  the  non- 
zinc  amalgam. 

While  the  strength  of  amalgam  contain- 
ing zinc,  or  other  impurities,  may  be  suffi- 
cient to  resist  fracture,  it  must  be  remem- 
bered that  strength  is  the  only  safeguard 
against  flow  and  that  resistance  of  amalgam 
to  flow  is  increased  as  the  strength  increases. 

The  result  of  these  tests  for  strength,  as 
well  as  any  other  tests  outlined  in  this 
article,  may  be  verified  by  any  individual 
dentist  or  any  study  club  of  dentists  and 
all  possible  assistance  in  making  the  tests 
will  be  given  by  the  publishers. 

Corrosion 

A  consideration  of  the  effect  of  zinc  on 
dental  amalgam  alloys  requires  some  ex- 
planation of  the  phenomena  of  corrosion 
of  alloys.  The  process  of  corrosion  may 
take  place  in  several  ways.     The  simplest 


of  these  may  be  described  as  chemical  cor- 
rosion in  which  the  alloj'  is  merely  dissolved 
in  the  Kquid,  in  the  same  way  that  a  simple 
metal  is  dissolved  in  an  acid,  as  zinc  in 
an  organic  acid. 

A  more  complicated  process  of  corrosion 
occurs  from  the  combined  influence  of  a 
corrosive  liquid  and  the  atmosphere.  This 
occurs  very  commonly  and  is  frequently 
observed  in  the  case  of  copper-zinc  alloys. 
The  maximum  effect  of  the  corrosion  takes 
place  at  the  surface  of  the  Uquid,  or  when 
the  metal  is  alternately  immersed  in  the 
liquid  and  exposed  to  the  air. 

Perhaps  the  most  interesting  as  well 
as  the  commonest  type  of  corrosion  is  that 
which  may  be  described  as  electrochemical. 
This  occurs  when  two  bodies  possessing 
different  electrical  properties  are  immersed 
in  contact  with  one  another  in  a  corrosive 
or  conducting  fluid.  Owing  to  the  difference 
of  potential  between  the  two  bodies,  an 
electromotive  force  is  set  up,  or  in  other 
words  a  galvanic  battery  is  formed  and 
one  of  the  bodies  passes  into  solution. 

As  zinc  is  electropositive  to  the  other 
metals  used  in  dental  amalgam  alloys,  we 
have,  when  the  alloy  is  amalgamated  and 
placed  in  the  mouth,  all  the  necessary  con- 
ditions to  produce  electrochemical  corro- 
sion. The  zinc  is  in  contact  with  the  other 
metals  of  the  amalgam,  immersed  in  a  con- 
ducting fluid,  the  saliva,  and  is  dissolved 
from  the  amalgam,  leaving  pits  and  net- 
work oxidation. 

The  voltage  between  zinc  and  any  of 
the  negative  elements  found  in  dental 
amalgams  may  be  found  by  adding  their 
single  potentials  as  found  in  the  table  of 
physical  properties  or  the  table  on  page  22. 
The  voltage  between  zinc  and  silver,  for 
instance  is  .493Y  plus  1.075V,  which  equals 
1.568V. 


[23] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


Galvanometer  Tests 

To  show  the  existence  of  electric  currents, 
local  action,  and  electrochemical  corrosion 
of  dental  amalgams  containing  zinc,  the 
following  tests  were  made  with  the  aid 
of  the  set  up  shown  in  Figures  22  and  23. 
This  is  an  accurate  galvanometer  and  two 
copper  wires  by  means  of  which  contact 
is  made  with  a  specimen  of  amalgam  held 
in  the  mouth  and  a  gold  crown  in  the 
same  mouth. 

Amalgam  cylinders  about  the  size  of 
the  crown  of  a  tooth  were  made  up  from 
the  most  widely  known  zinc  alloys,  accord- 
ing to  directions  given  for  those  alloys. 
Upon  making  connections  the  one  per 
cent  zinc  alloy  amalgams  gave  a  deflec- 
tion, as  shown  in  Figure  22,  ranging  from 
20  millivolts  to  beyond  the  largest  scale 
division  of  the  galvanometer,  which  is  25 
millivolts.     In  marked  contrast  the  non- 


Figure  23  —  The  deflection,  when  contact 
is  made  with  a  specimen  of  amalgam  made 
from  a  non-zinc  alloy  and  a  gold  crown, 
is  hardly  discernible,  ranging  from  1.75 
to  2  millivolts. 


Figure  22  —  A  galvanometer  with  contact 
made  with  a  specimen  of  amalgam  made 
from  a  zinc  alloy  and  with  a  gold  crown. 
In  a  series  of  tests  the  deflection  ranged 
from  twenty  to  twenty-five  millivolts. 

zinc  alloy  amalgam  gave  a  deflection  of 
only  1.75  to  2  millivolts,  as  shown  in 
Figure  23.  In  time  a  smaller  deflection 
results  due  to  polarization  or  coating  of 
one  electrode  with  hydrogen  and  in  the 
case  of  zinc  to  local  action  between  the 
metals  contained  in  the  one  amalgam.  This 
local  action  practically  short  circuits  the 
cell  (zinc  alloy  amalgam  vs.  gold)  so  that 
the  galvanometer  receives  only  a  portion 
of  the  original  current,  resulting  in  a  lesser 
deflection.  The  consumption  of  zinc  from 
the  amalgam,  due  to  this  galvanic  action, 
is  accompanied  by  pits  and  network  oxi- 
dation, as  previously  described. 

Galvanic  shock  is  frequently  experienced 
when  a  fork  or  spoon  comes  in  contact 
with  an  amalgam  filling  or  the  familiar 
electric  tingle  may  be  experienced  by  in- 
serting the  tongue  between  a  sheet  of 
zinc  and  a  piece  of  silver,  such  as  a  silver 
coin,  placed  in  contact. 


[24] 


EFFECT 


O    F 


ZINC 


O   N 


AMALGAM 


ALLOYS 


Eutectics  and  Impurities 

An  alloy  whose  constituents  separate 
on  cooling,  or  form  eutectics  which  separate 
on  cooHng,  will  almost  certainly  be  corroded 
on  account  of  the  difference  in  electric 
potential  between  the  constituents.  It  is 
for  this  reason  that  alloys  forming  solid 
solutions  are  usually  better  able  to  resist 
corrosion  than  highly  eutectiferous  alloys. 
Figure  24  shows  the  large  proportion  of 
eutectic  in  an  alloy  containing  1  per  cent 
of  zinc. 

Impurities,  such  as  dross,  slag,  oxides, 
etc.,  due  to  improper  treatment  of  the 
alloy,  are  the  cause  of  a  similar  form  of 
corrosion.  The  influence  of  impurities  on 
corrosion  has  received  more  attention  in 
the  case  of  metals  than  in  the  case  of  alloys. 
It  is  well  known  that  many  metals  in  a 
pure  state  are  only  soluble  with  difficulty 
in  acids,  while  the  same  metals  in  an  impure 
state  are  readily  soluble  in  the  same  acids. 

FINDINGS  BASED  UPON  FACTS 

In  addition  to  Dr.  Black's  and  Dr. 
McCauley's  charges  of  change  of  bulk,  it 
would  seem  that  the  charge  of  responsi- 
bility for  loss  of  strength,  for  pitting,  cor- 
rosion, and  galvanic  shock,  are  amply 
sustained  by  the  evidence.  We  conclude, 
therefore,  that  a  comparison  of  the  physical 
and  chemical  quahties  of  the  metals  con- 
sidered, indicates  that  only  silver,  tin,  and 
copper  should  be  used  for  dental  amalgam 
alloys,  that  gold  does  not  add  desirable 
properties,  and  that  zinc  is  inadmissible. 

Preparation  of  Dental  Amalgam  Alloys 

Having  determined  the  metals  which  are 
suitable  for  dental  amalgam  alloys,  there 
remains  the  determination  of  a  method  for 
combining  them  in  such  proportions  that 
their  desirable  properties  shall  be  retained 


and  their  undesirable  features  eliminated 
or  minimized. 

Many  methods  for  the  preparation  of 
dental  amalgam  alloys  have  been  detailed 
and  many  theories  of  abstruse  interest 
have  been  expounded,  but  the  one  prin- 
ciple which  has  proved  to  have  scientific 


Figure  24  —  The  eutectic  structure  of  a 
dental  amalgam  alloy  containing  1  per 
cent  of  zinc. 

and  practical  value  is  that  of  balancing 
molecular  movements.  Dr.  Black  was 
the  first  to  devise  an  amalgam  micrometer 
sufficiently  accurate  to  determine  the 
balancing  principle  as  the  correct  one  for 
alloying  silver  and  tin  in  such  proportions 
that  shrinkage  would  be  eliminated.  Vari- 
ous efforts  had  previously  been  made  to 
determine  the  shrinkage  or  expansion  of 
amalgam,  both  by  the  specific  gravity  test 
and  by  means  of  direct  reading  instruments, 
but  these  experiments  were  not  carried  to 
a  point  where  authoritative  results  were 
secured,  and  had  little  practical  value  in 
improAdng  the  quality  of  alloj's  ofl'ered  to 
the  profession. 

The  following  experiments  to  determine 
the   proportions  in   which   silver   and   tin 


[25] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


should  be  combined  to  effect  a  balance 
between  their  diametrically  opposed  quali- 
ties are  only  corroborative  of  Dr.  Black's 

work. 

AMALGAM  MICROMETERS 

Figure  25  shows  the  micrometer  used  by 
Dr.  Black  in  his  research  upon  amalgam. 
The  smallest  divisions  are  0.0001  inch  and 


Figure  25 — Dr.  Black's  Amalgam  Microm- 
eter. Unit  of  measurement  0.0001.  (From 
Black's  "Operative  Dentistry,"  Vol.  II.) 

the  microscope  is  used  separately  to  check 
the  readings  of  the  micrometer. 

The  micrometer  used  by  Dr.  Black  has 
been  replaced,  for  these  experiments,  by 
a  micro-micrometer  of  original  design,  which 
is  the  most  exact  and  delicate  instrument 
ever  used  for  the  measurement  of  the 
volume  changes  of  amalgam.  As  shown 
in  Figure  26,  it  is  a  combination  of  microm- 


eter mechanism  with  the  powerful  micro- 
scope. Four  revolutions  of  the  calibrated 
wheel  measure  one  millimeter,  the  wheel 
bears  250  divisions,  thus  the  least  count 
is  0.001  millimeter,  one  micron,  or  0.00004 
inch.  With  careful  work  readings  may  be 
made  as  fine  as  0.1  micron,  or  0.000004 
inch,  and  these  readings  may  be  repeated, 
moving  the  instrument  in  either  direction. 
In  checking  tests  made  with  micrometers 
of  other  design,  we  find  that  they  often 
give  inaccurate  results  because  of  friction, 
lost  motion,  complex  design,  and  errors  in 
calibration. 

The  Wedelstaedt  tubes,  shown  at  the 
left  of  the  micro-micrometer  and  in  Figure 
27,  are  those  standard  in  making  amalgam 
tests.  They  are  hardened  steel  tubes  with 
a  definite  diameter  and  depth.  The  cavity 
is  grooved  at  the  bottom  so  that  the 
amalgam,  when  condensed  in  it,  will 
be  held  from  moving  away  from  the  base. 
While  the  amalgam  is  still  plastic,  a  hard- 
ened and  polished  steel  point  is  placed  at 
the  center  of  the  filling.  The  touch  point 
of  the  micro-micrometer  makes  contact 
with  this  and  communicates  the  amount 
of  expansion  or  contraction.  If  the  amal- 
gam expands,  it  can  not  change  the  form 
of  these  tubes,  on  account  of  their  strength, 
but  is  necessarily  forced  to  protrude  from 
the  cavity. 

Figure  27  shows  empty  and  filled 
W^edelstaedt  tubes.  These  tubes  fit  into 
the  micro-micrometer  and  are  locked  in 
such  a  way  that  they  may  be  removed  and 
replaced,  at  any  time,  in  their  exact 
original  position.  This  is  an  essential 
factor   in   securing   accurate   results   in   a 


[26] 


PREPARATION        OF       DENTAL       AMALGAM       ALLOYS 


series  of  tests  which  is  to  be  carried  over 
a  period  of  several  months  and  leaves  the 
instrument  available,  in  the  meantime,  for 
other  tests. 

To  further  substantiate  the  readings  of 
the  micro-micrometer,  the  test  filling  is 
placed  in  a  sliding  rack,  under  the  objective, 
and  the  margins  about  the  tube  are 
examined  with  the  aid  of  reflected  arti- 
ficial light.  In  case  of  shrinkage  of  the 
amalgam,  the  width  of  the  ditch  between 
the  amalgam  and  the  tube  can  be  measured. 


BALANCING 

To  determine  the  composition  at  which 
the  shrinkage  of  the  tin  amalgam  offsets 
the  expansion  of  the  silver  amalgam,  the 
following  tests  were  made: 

An  alloy  containing  40  per  cent  silver 
and  60  per  cent  tin  was  amalgamated, 
according  to  the  usual  technic,  and  con- 
densed in  Wedelstaedt  tubes.  A  touch 
point  of  polished  steel  was  placed  in  the 
center  of  the  filling,  the  tube  was  inserted 
in  the  micro-micrometer,  and  measure- 
ments were  taken  and  recorded.     As  the 


Figure  26 
Dr.  Crandall's  Amalgam  Micro-Micrometer,  least  count  0.00004  inch. 


[27] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


amalgam  continued  to  harden,  successive 
readings    were    recorded    at    five    minute 
intervals  for  a  period  of  one  hour,  then  at 
successive    lengthening    intervals.      These 
readings    indicated    excessive    shrinkage. 
A  filling  was  next  made  from  an  allo^'  of 
the  formula  45  i>er  cent  silver,  55  per  cent 
tin:  shrinkage  was  still  present,  but  was  a 
Kttle  less  than  before.     These  tests  were 
continued  by  advancing  the  silver  content 
of  the  alloy  5  per 
cent    each    time, 
unto  the  ratio  65 
per    cent    silver. 
35   per    cent    tin 
was  reached.    At 
this  point,  fillings 
made  from  fresh 
cut    filings    gave 
two   microns   ex- 
pansion,    while 
fillings      which 
were  made   from 
annealed  filings 
gave  twenty -seven  microns  shrinkage. 

As  alloys  have  the  property  of  aging, 
or  undergoing  poh-morphic  change,  further 
research  was  conducted  upon  aged  or 
annealed  alloys.  At  70  per  cent  silver, 
30  per  cent  tin,  the  shrinkage  was  fifteen 
microns,  at  75  per  cent  silver.  25  per  cent 
tin,  an  expansion  of  twenty-eight  microns 
was  noted  at  the  end  of  two  hours,  followed 
by  a  shght  contraction,  resulting  in  a  final 
expansion  of  24.5  microns.  The  silver 
content  was  next  reduced  in  stages  of 
0.1  per  cent  until,  at  74.3  per  cent  an 
expansion  of  three  microns  was  noted 
after  a  period  of  five  days. 

In  a  manner  entirely  analagous  to  this, 
the  point  of  balance  must  be  redetermined 
when  copper  is  introduced  into  the  alloy. 
When  the  point  of  balance  is  determined, 


£♦ 


B 


A 


A  and  B,  empty; 
filling,    sho'Ting 


Figure  27  —  Wedelstaedt  Tubes. 

C,  tube  with  test  filling;   D,   te 

great  expansion;  E,  steel  tube  used  to  standardize 

the  micro-micrometer  to  varying  temperatures;  F, 

side  view  of  tube,  showing  guiding  slot 


it  holds  good  only  for  the  lot  of  metals 
tested.  Variations  in  the  purity  of  metals 
obtainable,  variations  in  heat  treatment 
which  they  have  received,  vart'ing  methods 
by  which  they  have  been  manipulated,  and 
other  factors  necessitate  the  determina- 
tion of  the  fineness  of  even,^  lot  of  metals 
procured  and  micro-micrometer  tests  of 
everj'  lot  of  the  finished  product. 

It  is  e\'ident  that  the  determination  of 
the  balance  point 
for    each    lot    of 
metals  is  the  onlj^ 
accurate    method 
of  arriving  at  cor- 
rect    proportions 
to  produce  a  bal- 
anced   alloy.      If 
the    alloj^   is    de- 
ficient in  silver  as 
much  as  0.1  per 
cent  a  shrinkage 
of    five    microns 
may  occur  about 
the  margins  of  large  ca\ities.  This  would 
ob^doush"  destroy  the  utiUtj^  of  the  restora- 
tion, regardless  of  the  quahty  of  the  technic 
emploj^ed. 

One  micron,  as  determined  b}'  micro- 
micrometer  measurement,  corresponds  to 
a  ditch  or  space  0.00004  inch  in  width, 
between  the  fiUing  and  the  ca\dt3'  wall. 
The  micro-organisms  productive  of  caries 
varj^  in  size  from  0.4  micron  to  0.8  micron. 
If  the  width  of  the  ditch,  5  microns, 
is  divided  by  the  diameter  of  the  bacteria, 
0.4  or  0.8  micron,  it  will  be  seen  that  a 
small  army  of  these  bacteria  could  march 
into  the  space  from  six  to  twelve  abreast. 
Recurrence  of  caries  must  attend  this 
invasion  of  bacteria.  We  leave  for  j^our 
consideration  the  possibOities  which  may 
occur  with  those  alloys  which  show  a  con- 


[28] 


PREPARATION        OF        DENTAL       AMALGAM       ALLOYS 


traction  of  from  ten  to  seventy-five  microns. 
Without  the  aid  of  precision  instruments 
which  will  detect  the  minutest  movements 
of  an  amalgam  while  it  is  hardening,  it  is 
impossible  for  the  manufacturer  to  give 
assurance  of  a  desirably  balanced  alloy. 

The  Proximate  Analysis  of  Alloys 

The  physical  properties  of  alloys  which 
give  them  their  industrial  importance  de- 
pend largely  upon  their  proximate  compo- 
sition, or  constitution,  as  revealed  by 
thermal  analysis  and  microscopical  exami- 
nation. The  chemist  reports  the  anah'sis 
of  brass,  for  instance,  as  70  per  cent 
copper,  30  per  cent  zinc,  while  the  report 
of  the  metallographist  is  concerned  with 
such  data  as  the  character  and  distribution 
of  the  solid  solutions,  defects  in  the  metal, 
heat  treatment,  mechanical  defects,  results 
of  strength  of  materials  tests,  grain  struc- 
ture, extent  of  deformation,  and  bene- 
ficial modifications  in  composition  or  pro- 
duction. 

In  the  great  majority  of  cases,  two  or 
more  metals  can  be  mixed  with  one  another, 
in  the  molten  condition,  in  any  relative 
proportion,  and  in  a  manner  analagous  to 
the  formation  of  well  known  organic  or 
inorganic  solutions.  However,  compounds 
may  form,  and  metals  varying  widely  in 
such  physical  properties  as  melting  point 
may  form  mutual  solutions  to  such  a 
slight  extent  as  to  be  practically  immiscible. 

According  to  the  number  of  metals  con- 
tained in  the  series,  alloys  are  classified 
into  binary,  ternary,  and  higher  systems; 
while,  according  to  their  behavior  in  the 
molten  state  and  upon  soUdification,  they 
are  classified  as  chemical  compounds, 
solid  solutions,  and  eutectics. 

CHEMICAL  COMPOUNDS 

The  chemical  compounds  of  one  metal 
with  another  do  not,  in  general,  follow  the 


law  of  valence,  but  are  of  the  type  known 
as  molecular.  The  resulting  chemical  com- 
pound differs  much  less  in  its  properties 
from  those  of  its  component  metals  than 
is  the  case  with  strong  chemical  compounds. 
It  is  in  accordance  with  this  general  idea 
that  it  is  concluded  that  even  those  metals 
which  do  form  definite  chemical  com- 
pounds are  relatively  feebly  combined.  The 
metallic  compounds  usually  have  a  limited 
range  of  stability  and  at  certain  points 
in  the  equihbrium  diagram  are  resolved 
into  other  bodies.  Great  difiiculty  is 
experienced  in  isolating  most  of  these 
compounds  and  the  chemical  constitution 
of  comparativeh^  few  of  them  has  been 
determined  with  certainty. 

The  evidence  for  considering  that  a 
structural  constituent  is  a  definite  com- 
bination of  two  metals,  instead  of  a  soKd 


Figure  28  —  Photomicrograph  of  Ag^Sn, 
a  well  established  metallic  chemical  com- 
pound. 

solution,  is  not  always  as  conclusive  as 
would  be  desirable.  On  the  hquidus  the 
formation  of  a  compound  is  often  indicated 
by  a  sudden  change  of  curvature  and  the 
whole  range  of  composition  throughout 
which  the  compound  separates  from  the 


[29] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


liquid  mixture  corresponds  to  a  distinctly 
separate  branch  of  the  liquidus.  At  other 
times  the  change  of  curvature  is  almost  or 
(luite  indistino-uishablc,  but  in  this  case 
the  compound  usually  forms  solid  solutions 
with  the  component  metals,  or  with  other 
compounds  of  the  series,  and  can  not  be 
isolated.     When  the  occurrence  of  a  com- 


Figure    29  —  Cold-rolled    brass,    a    well 
known  example  of  metals  in  solid  solution. 


pound  is  shown  by  a  distinct  branch  of  the 
liquidus,  this  frequently  exhibits  a  point 
of  maximum  temperature,  which  is  the 
freezing  point  of  the  pure  compound.  The 
composition  of  the  mixture  which  shows 
this  maximum  freezing  point  is  difficult 
to  determine  with  exactness,  since  the 
curve  is  somewhat  flat,  but  it  is  found  to 
agree  closely  with  a  simple  atomic  propor- 
tion of  the  two  metals.  Under  the  micro- 
scope this  compound  is  distinguished  as  a 
new  structural  constituent  which  differs 
in  properties,  such  as  color,  hardness,  and 
rate  of  etching,  from  the  component  metals, 
eutectic,  or  solid  solution.  At  a  certain 
composition  the  whole  of  the  section 
appears  to  consist  of  this  new  constituent 
and,  if  analyzed,  the  alloy  is  found  to 
contain  the  metals  in  proportions  corre- 
sponding very  nearly  wdth  those  represented 
by  the  peak  of  the  Uquidus  curve.     It  is 


reasonable  to  suppose  that  a  chemical  com- 
bination of  the  metals  in  a  series  of  alloys 
exists  only  when  — 

1.  At  a  certain  composition,  it  consti- 
tutes the  whole  of  a  just  solid  metal; 

2.  On  chemical  analysis  is  found  to  con- 
tain the  metals  in  approximately  simple 
atomic    proportions; 

3.  Gives  rise  to  a  separate  branch  of 
the  liquidus  curve,  showing  a  temperature 
maximum  at  a  composition  very  close  to 
that  given  by  analysis; 

4.  Has  physical  properties  such  as  color, 
hardness,  density,  electrical  conductivity, 
etc..  which  differ  sharply-  from  other  struc- 
tural constituents  of  the  series. 

A  well  established  metallic  chemical 
compound  which  fulfills  all  these  condi- 
tions is  Ag.^Sn.  A  photomicrograph  of 
this  compound  is  shown  in  Figure  28. 

While  a  number  of  ])inary  metallic  com- 
pounds have  been  established,  according  to 
Dr.  Rosenhain  no  ternary  metallic  com- 
pounds have  been  determined  to  date. 

SOLID  SOLUTIONS 

The  distinguishing  characteristic  of  a 
solution  is  that  the  particles  of  the  dissolved 
substance  can  not  be  detected  and  can  not 
be  separated  by  mechanical  means.  For 
example,  in  a  mass  of  copper  containing 
tin,  the  tin  can  not  be  detected  under  a 
microscope  of  the  highest  powers,  nor  can 
it  be  separated  by  mechanical  means.  The 
allo\^  solidifies  and  crystallizes  as  though  it 
were  a  pure  metal  and  the  mixture  of  the 
two  metals  is  so  intimate  that  there  is  a 
strong  analogy  between  it  and  a  liquid 
solution. 

Examples  of  metallic  solid  solutions  of 
wide  industrial  use  are  shown  in  the  photo- 
micrographs of  cold  rolled  brass,  Figure 
29,  and  copper-tin  alloy,  Figure  30.     The 


[30] 


PREPARATION        OF        DENTAL        AMALGAM        ALLOYS 


latter  is  an  alloy  of  tliQ  bronze  series  which 
was  cooled  too  rapidly  for  the  beta  to 
gamma  transformation  to  take  place.  The 
black  areas  represent  primary  crystal 
skeletons  of  beta,  chilled  at  725°  C.  The 
particular  solid  solutions,  i.e.,  alpha,  beta, 
gamma  or  delta,  found  in  this  series  of 
alloys,  have  a  very  important  effect  upon 
physical  properties. 

Mechanism  of  the  Formation  of  Solid  Solutions  of 
Two  Metals 

Let  us  assume  that  a  certain  proportion 
of  the  metal  tin,  of  relatively  low  melting 
point,  is  alloyed  with,  or  dissolved  in,  the 
metal  copper  which  has  a  higher  melting 
point.  The  copper  may  be  considered  as 
the  solute  and  the  tin,  as  the  solvent.  It 
is  believed  that,  when  solidification  begins, 
homogeneous  crystals  of  tin  and  copper 
are  formed,  but  that  they  contain  a  smaller 
proportion  of  the  fusible  metal,  tin,  than 
the  liquid  bath,  which  is  thereby  enriched 
in  tin.  On  further  cooling  these  crystals 
grow,  but  the  crystalline  matter  now 
deposited  contains  more  of  the  metal  tin 
than  the  crystals  first  formed,  although 
still  less  than  the  molten  bath  which  is 
further  enriched  in  tin,  and  so  on,  the 
crystals  growing  through  successive  ad- 
ditions of  crystalline  matter,  containing 
increasing  proportions  of  the  dissolved  and 
readily  fusible  tin,  and  approaching,  there- 
fore, although  not  reaching  the  composi- 
tion of  the  molten  metal,  until  finally  the 
last  drop  sohdifies.  A  homogenizing  an- 
neal will  bring  the  whole  mass  to  the  same 
composition. 

Figures  31,  32,  33  and  34  show  a  balanced 
silver-tin-copper  alloy  in  process  of  homo- 
genization.  Figure  31  shows  the  dendritic 
structure  of  the  alloy  upon  solidification, 
while  Figure  34  shows  the  completely 
homogenized    alloy.      Figures    32    and    33 


are    intermediate    stages     during    homo- 

genization. 

EUTECTICS 

The  eutectic  is  a  conglomerate  of  metals, 
has  a  constant  composition,  always  freezes 
at  the  same  temperature,  and  is  the  lowest 
freezing  alloy  which  can  be  obtained  in  the 
series.  The  eutectic  structure  is  composed 
of  the  different  constituents  in  juxtaposi- 
tion. The  constituents  of  a  eutectic  may 
occur  in  curved  plates  or  laminae,  or  in 
globules,  and  either  or  both  may  be  simple 
metals,  solid  solutions,  or  compounds. 
Types  of  eutectic  structure  are  shown  in 
Figures  35  and  36 ;  they  are  very  character- 
istic and  are  not  easily  mistaken. 

The  manner  of  employing  cooling  curves 
in  the  construction  of  the  equilibrium  dia- 


Figure  30  —  Another  example  of  metals 
in  solid  solution.  Copper-tin  alloy,  73 
per  cent  copper,  magnified  45  diameters, 
etched  with  acidified  ferric  chloride. 

gram  for  a  eutectiferous  series,  is  shown  in 
Figure  37.  The  eutectic  E  has  the  longest 
eutectic  halt,  corresponding  to  the  greatest 
evolution  of  heat  on  cooling.  The  other 
alloys  of  the  series  evolve  an  amount  of 
heat  at  the  eutectic  temperature  propor- 


[31] 


STANDARDIZING         THE         AMALGAM         FILLING 


tional   to   the   amount   of  eutectic   which 
they  contain. 

In  the  ternary  dental  amalgam  alloy, 
silver-copper-tin,  properly  balanced,  the 
copper  content  should  be  within  the  solid 
solution  range,  and  the  tin  content  small 


Figure  31 — A  balanced  silver-tin-copper 
alloy  remelted  and  slowly  cooled,  showing 
solid  solution. 

enough  to  prevent  extensive  formation  of 
eutectic.  The  silver  content  should  be 
sufficiently  high  to  form  the  strongest 
primary  freezing  amalgam  network.  Ther- 
mal analysis  and  photomicrographs  are 
used  to  indicate  the  proportion  of  eutectic 
and  solid  solutions,  the  latter  being  the 
desirable  constituent  of  dental  amalgam 
alloys.  Silver  can  not  be  reduced  beyond 
a  certain  point  without  producing  an  alloy 
which  is  highly  eutectiferous  and  weak 
upon    amalgamation. 

Aging  and  Annealing  of  Dental  Amalgam 

Alloys 

Annealing,  and  heat  treatment  in  general, 
effects  profound  changes  in  the  physical 
properties  of  alloys.  The  freshly  cut  dental 
amalgam  alloys  require  a  high   percentage 


of  mercury  for  their  amalgamation,  and  are 
so  extremely  rapid  setting  that  very  few 
operators  are  able  to  emploj'  them  satis- 
factorily. Aimealed  alloys  require  less  mer- 
cury and  are  modified  in  their  setting 
qualities  so  that  they  may  be  correctly 
manipulated. 

DR.  BLACK'S  EXPERIMENTS 

After  a  series  of  experiments  which  are 
outhned  on  page  308,  Volume  II,  "Opera- 
tive Dentistr}^,"  Dr.  Black  reached  the 
following  conclusion  in  regard  to  the 
changes  produced  in  alloys  by  annealing: 

"Conclusion:  The  cut  alloy  is  made 
abnormally  hard  by  the  violence  in  cutting, 
the  same  as  metals  are  made  hard  by  ham- 
mering. By  the  processes  above  detailed, 
it    becomes    annealed    to    normal.      The 


Figure  32  —  A  balanced  silver-tin-copper 
alloy  partly  homogenized. 


change  was  produced  by  heat.  This 
effects  a  change  in  the  affinity  for  mercury 
and  the  rapidity  of  combination  with  the 
results  named  above.  Why,  is  unknown, 
but  the  Jact  stands  all  tests.  It  is  a  primary 
physical  phenomenon." 


[32] 


PREPARATION        OF       DENTAL       AMALGAM       ALLOYS 


FURTHER  RESEARCH  UPON  AGING 
PHENOMENA 

Incidental  to  our  research  upon  dental 
alloys  and  amalgams,  the  following  obser- 
vations have  been  made.  It  would  seem 
that  they  offer  a  reasonable  explanation  of 
the  slower  rate  of  amalgamation  which 
characterizes  aged  fihngs  of  dental  amal- 
gam alloys. 

Freshly  cut  alloy  is  rapid  setting  for  a 
number  of  reasons,  chemical,  physical,  and 
physico-chemical.  The  particles  from  the 
cast  ingot  are  in  a  state  of  metastable 
equilibrium,  due  to  suspended  transfor- 
mation of  part  of  the  alloy  into  the  normal 
proportions  of  compound,  solid  solution, 
and  eutectic. 

Filing,  or  cold  work,  endows  the  freshly 
cut  particles  with  strain  potential  which, 


Figure  33  —  Another  stage  in  the  homo- 
genization  of  a  balanced  silver-tin-copper 
alloy. 

according  to  the  electrolytic  theory  of 
solution,  favors  more  rapid  amalgamation. 
In  order  to  better  understand  the  effect  of 
cold  work  and  annealing,  it  should  be 
pointed  out  that  the  structure  of  metals  is 
crystalline. 


It  appears  that  the  particles  of  freshly 
cut  alloy  are  full  of  cracks,  thus  presenting 
more  surface  to  the  attack  of  mercury  or, 
more  accurately,  the  severely  strained 
metal  has  developed  a  finer  crystalhne 
structure  and,  of  course,  the  fine  crystals 


'^      ^                           '  * 

',-  \  ' 

'■'■'""-       •               ■     : 

*V    "■-^"'       *''       y  ■■"■      -       -.1 

U^V-  .:^;^J.--  ^ :  ■    -•-^'■,  "-'  -  ' 

~-  «-\-"*^' .-'-.-,-     ' '  J    -"-  -"    '  •    ■ 

* 

-:■-'   ^              ■*. 

i^^^^#f:-..;--v- 

^^\^-  -^ 

Figure  34  —  A  balanced  silver-tin-copper 
alloy  fully  homogenized. 

will  dissolve  more  rapidly  in  mercury  than 
the  same  amount  of  material  in  the  form 
of  large  crystals,  or  crystals  of  a  more 
resistant  system. 

Changes  in  temperature  and  pressure 
frequently  give  rise  to  different  crystal 
structures  and  change  in  physical  state,  or 
molecular  arrangement,  is  accompanied  by 
alterations  in  physical  properties.  When 
metals  or  alloys  are  severely  strained  by 
compression,  tension,  or  bending,  the 
original  crystals  are  broken  up  and  re- 
placed by  much  finer  units.  Microscopical 
examination  of  a  metal  strained  beyond 
the  elastic  limit  reveals  fine  hnes  on  the 
crystal  grains  termed  sUp  bands.  These 
sHp  bands  are  cleavage  planes,  for  the 
most  part  intimately  connected  with  the 
formation  of  new  small  crystals. 


[33] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


UNAGING  AN  AGED  ALLOY 

Alloy  which  had  been  aged  by  annealing 
was  unaged,  during  these  experiments, 
after  repeated  grinding  in  a  mortar  fol- 
lowed   by    heavy    pressure    exerted    by    a 


^3©3 


r***^? 


Figure   35  —  Photomicrograph   of   silver- 
copper  eutectic. 

modified  Brinnel  machine.  The  freshly 
cut  allo}^  amalgamated  with  equal  parts 
of  mercury  was  quick  setting  and  only  a 
minimum  of  mercury  could  be  expressed 
in  a  vise  after  amalgamating.  The  annealed 
alloy  was  slower  setting  and  much  more 
mercur}^  was  expressed  with  the  same 
amount  of  pressure  applied  with  a  vise. 
After  the  annealed  alloy  had  been  subjected 
to  the  grinding  and  heavy  pressure  men- 
tioned, it  reassumed  the  properties  of  a 
freshly  cut  alloy,  in  regard  to  time  of  setting 
and  the  amount  of  mercury  which  it  was 
possible  to  express  in  a  vise  after  amal- 
gamation. 


The  appearance  of  "amorphous  layers" 
marks  an  increase  in  the  following  physical 
properties:  hardness,  tensile  strength,  vol- 
ume, heat  of  solution,  and  solution  pressure. 

Amorphous  material  etches  and  amal- 
gamates more  rapidly  than  crystalline  or 
annealed  metal.  Howe  states  that,  "The 
plasticall}'  deformed  metal  etches  faster 
because,  being  lighter,  that  is  bulkier  and 
less  closely  packed,  it  offers  greater  surface 
for  attack;  because  its  amorphous  metal 
lacks  crystalline  bond  which  in  itself 
opposes  solution  and  every  other  kind  of 
attack;  and  because  in  being  a  mechanical 
mixture  of  amorphous  and  crystalline 
metal,  it  has  local  differences  of  potential, 
which  are  such  frequent  accelerators  of 
corrosion." 

Our  dissolving  agent  is  mercury  and, 
digressing,  we  have  found  it  to  be  a  valu- 


Figure  36  —  Copper-Antimony  eutectic. 
TMs  illustration  and  Figure  35  show 
characteristic  eutectic  structure. 


AMORPHOUS  MATERIAL 

Another  important  factor  affecting  a 
freshly  cut  alloy  is  the  formation  of  so- 
called  "amorphous  material,"  upon  filing 
or   severely  straining  by   heavy  pressure. 


able  etching  reagent,  which  enables  us  to 
watch  the  growth  of  amalgam  crystals 
under  the  microscope,  and  to  bring  out 
upon  a  polished  surface  constituents  of 
an  alloy  not  readily  amalgamated. 


[34] 


PREPARATION       OF       DENTAL       AMALGAM       ALLOYS 


ANNEALING 

If  thorough  amalgamation  took  place, 
equilibrium  conditions  in  the  alloy  filings 
would  be  of  less  importance,  but  as  a 
matter  of  fact  partial  amalgamation  takes 
place  and  the  alloy  particles  are  enveloped 
with  amalgam,  and  not  completely  dis- 
solved. 

In  order  that  the  balance  point  of  an 
alloy  may  remain  constant  for  at  least  a 
year,  it  has  been  found  advisable  to  anneal, 
or  age,  the  filings  in  a  manner  determined 
by  careful  experiment.  This  heat  treat- 
ment reduces  the  setting  rate  of  a  high 
grade  alloy  so  that  it  comes  within  the 
range  of  careful  manipulation,  makes 
possible  the  use  of  a  lower  percentage  of 
mercury  and  reduces  the  amount  of 
expansion  of  the  alloy  upon  amalgamation. 

The  effective  annealing  period  and  tem- 
perature is  a  function  of  the  chemical 
elements  of  which  the  alloy  is  composed 
and  also  of  the  proportions  of  its  structural 
constituents.  The  proper  annealing  tem- 
perature and  period  must  be  determined 
for  each  alloy  in  order  to  obtain  the  par- 
ticular condition  desired. 

OVERANNEALING 

Overannealing  enlarges  the  crystalline 
grains  of  the  alloy,  reducing  its  strength, 
and  affecting  its  working  qualities  upon 
amalgamation.  This  change  may  take 
place  through  the  use  of  too  high  temper- 
ature for  a  short  period  of  time,  or  from 
exposure  to  ordinary  room  temperature 
over  a  longer  period  of  time. 

In  regard  to  this  change  Dr.  Black  says, 
in  "Operative  Dentistry,"  Volume  II,  page 
311: 

"Tubes  of  alloy  were  put  up  for  time 
tests,    some    of    which    yet    remain    after 


twelve  years,  and  frequent  tests  have  been 
made.  Shrinkage  and  expansion  remain 
unaffected.  The  amount  of  mercury  re- 
quired diminishes,  the  amalgamation  be- 
comes easier,  the  setting  becomes  slower, 
and  the  strength  of  the  amalgam  is  grad- 


Figure  37  shows  the  manner  in  which 
cooling  curves  are  employed  in  the  con- 
struction of  an  equilibrium  diagram  for  a 
eutectiferous  series. 

ually  reduced.  An  alloy  that  makes  a 
crisp  amalgam  which  sets  quickly,  such  as 
should  always  be  used  in  practice  will,  if 
kept  two  or  three  years  at  ordinary  room 
temperatures,  come  to  make  rather  a 
sloppy,  slow-setting  mass.  If  the  alloy 
is  exposed  to  the  heat  of  the  sun  or  other- 
wise to  unusually  high  temperatures,  these 
changes  will  be  rapid  in  proportion." 

CRUSHING  STRENGTH  OF  OVERAGED  ALLOY 

To  determine  the  loss  of  strength  of 
amalgam  made  from  overaged  alloy  a 
series  of  dynamometer  tests  has  been 
made  with  alloy  two  years  old.  Alloy 
and  mercury  were  used  in  equal  parts, 
heavy  mallet  force  was  used  for  condens- 
ing, and  some  excess  mercury  was  ex- 
pressed during  condensing.  The  average 
strength  shown  over  a  period  of  two  and 
one-half  months  was  348  pounds,  while 
tests  made  under  the  same  conditions 
with  alloy  less  than  one  year  old  showed 
a  crushing  strength  averaging  about  500 
pounds. 


[35] 


STANDARDIZING         THE         AMALGAM         FILLING 


We  conclude  that  dental  amalgam  alloys 
should  not  be  annealed  beyond  the  zero 
point,  except  for  cases  where  extremely 
slow  setting  alloys  may  be  desirable,  and 
where  the  strength  of  the  amalgam  is  not 
an  essential  factor.  As  even  low  temper- 
atures bring  about  this  change  if  continued 
over  a  long  period,  it  is  not  advisable  to 
use  alloys  which  have  been  manufactured 
for  a  considerable  length  of  time,  or  alloys 
of  which  the  date  of  manufacture  is 
unknown. 


Bibliography 
Metallography  —  Desch. 
Alloys  and  their  Industrial  Applications  — 

Law. 
The  Heat  Treatment  and  Metallography  of 

Iron  and  Steel  —  Howe. 
Metallic  Alloys  —  Gulliver. 
Physical  Metallurgy  —  Rosenhain. 
Practical  Alloying  —  Buchanan. 
Operative  Dentistry  —  Black. 
Dental  Cosmos. 


Section  III.    Amalgamation 


HAVING  considered  correct  cavity 
preparation  and  the  requisite  quali- 
ties of  dental  amalgam  alloys,  we  come  to 
the  third  essential  of  standardized  amal- 
gam technic,  correct  amalgamation,  of 
equal  importance  with  these  and  the 
succeeding  steps  of  the  operation.  Amal- 
gamation may  be  described  as  a  process 
of  melting  and  selective  freezing. 
SELECTIVE  FREEZING 
In  order  to  make  the  process  of  selective 
freezing  somewhat  clearer,  there  may  be 
constructed  a  hypothetical  binary  solid 
solution  diagram,  as  shown  in  Figure  38, 
considering  the  tin  amalgam  as  one  element 
and  the  silver  amalgam  as  the  other.  Let 
the  tin  amalgam  contain  30  per  cent 
mercury;  likewise,  the  silver  amalgam. 
Suppose  the  tin  amalgam  freezes  at  100°  C. 
and  the  silver  amalgam  at  400°  C.  Let  A- 
B  be  the  amalgam  under  consideration; 
at  K,  300°  C.,  a  drop  or  so  of  silver-rich 
solid  solution,  having  the  composition 
shown  at  0,  freezes  out;  the  remainder 
being  liquid.  This  selective  freezing  con- 
tinues until  the  last  drop  freezes  at  L,  175° 


C.,  having  the  composition  shown  at  N  or 
M.  Thus  the  resulting  alloy  froze  in  the 
area  KOLM;  it  will  show  core  structure 
and  consist  of  the  summation  of  alloys 
ranging  in  composition  from  O  to  M.  The 
primary  freezing  silver-rich  network,  or 
core  structure,  possesses  a  composition  in 
the  neighborhood  of  0;  the  crystalline 
grains  are  relatively  fine;  the  whole  is  a 
fairly  strong  structure.  This  represents  the 
amalgam  when  first  placed  in  the  mouth. 
Now  suppose  the  amalgam  to  be  at  blood 
heat  and  every  meal  up  to  the  temperature 
of  hot  drinks.  The  amalgam  becomes 
homogenized;  the  whole  returns  to  the 
composition  B;  the  grains  become  larger, 
weaker,  and  coarsely  crystalline;  the  proc- 
ess is  accompained  by  volume  change. 
This  change  is  the  more  readily  accom- 
plished the  larger  the  proportion  of  low 
melting  metal  or  eutectic. 

AMALGAM  MANIPULATION 

Dental  amalgams  are  partial  solutions  of 
a  metal  or  alloy  in  mercury;  the  state  and 
condition  of  the  solution  have  a  decided 
effect  upon  the  final  result  of  an  operation 


[36] 


AMALGAMATION 


O  F 


ALLOY 


AND 


MERCURY 


for  which  the  amalgam  is  used,  the  method 
of  manipulation  affects  the  result  to  an 
equal  degree. 

There  is  a  wide  variation  in  the  abihty 
of  dentists  to  manipulate  amalgam  and  an 
unwilHngness  on  the  part  of  some  to  spend 


Figure   38  —  Hypothetical  silver-tin-mer- 
cury Diagram. 

the  time  necessary  for  the  manipulation 
of  an  amalgam  made  from  a  balanced 
alloy.  Many  dentists  insist  upon  using 
alloys  which  produce  an  amalgam  which  is 
plastic  and  easily  manipulated,  although 
it  is  well  known  that  such  amalgams  do  not 
produce  permanent  results.  Neither  should 
an  alloy  be  used  if  its  amalgam  sets  so 
quickly  that  it  is  beyond  the  ability  of  the 
skillful  operator  to  manipulate  it.  Such 
alloys  require  high  percentages  of  mercury 
to  make  their  amalgam  sufficiently  plastic 


to  permit  good  manipulation,  and  it  may 
be  stated,  as  a  principle  of  amalgamation, 
that  the  strength  of  amalgam  varies 
inversely  with  the  mercury  content.  The 
best  alloys,  of  necessity,  make  a  rather 
quick-setting  amalgam,  but  it  is  possible 
to  regulate  their  setting  qualities  so  that 
any  operator  should  be  able  to  manipulate 
them  successfully. 

MERCURY 

Mercury  seems  to  affect  the  physical 
properties  of  most  metals  injuriously;  for 
instance,  if  mercury  is  alloyed  with  nickel, 
under  the  influence  of  heat  and  pressure, 
the  metal  develops  a  coarse  granular 
structure  and  will  not  bend,  as  formerly, 
without  breaking.  Fortunately  silver  and 
copper  require  larger  percentages  of  mercury 
than  those  used  in  ordinary  practice,  before 
their  valuable  properties  are  decreased 
beyond  the  permissible  limit. 

The  purity  of  the  mercury  used  is  a 
factor  in  the  success  of  an  amalgam  opera- 
tion, as  the  mercury  of  commerce  frequently 
contains,  in  addition  to  the  oxides  and 
sulphides  noted  as  scum  upon  the  surface, 
copper,  lead,  zinc,  or  tin,  which  when 
added  to  the  alloy  may  so  change  its  pro- 
portions that  the  permanent  usefulness  of 
any  operation  for  which  it  is  used  will  be 
destroyed. 

At  ordinary  temperatures  mercury  coats 
a  particle  of  alloy  and  forms  a  protecting 
or  uniting  envelope  of  amalgam,  while  very 
little  mercury  diffuses  to  the  center  and 
none  will  be  found  at  the  center  of  a  fairly 
large  specimen.  In  this  process,  termed 
partial  amalgamation,  there  is  a  gradient 
in  the  mercury  percentage  from  the 
mercury-rich  exterior  to  the  center  con- 
taining, perhaps,  none.  Figure  39  shows 
this  gradation  in  the  composition  of  an 
alloy  particle  partially  dissolved  in  mercury. 


[37] 


STANDARDIZING         THE         AMALGAM         FILLING 


PROPORTIONS    OF    MERCURY    AND    ALLOY 

The  correct  ratio  of  alloy  to  mercury  is 
an  essential  factor  in  the  final  result,  as 
an  excess  of  mercury  will  cause  a  shrinlcing 
alloy  to  shrink  more,  an  expanding  alloy 
to  expand  excessively,  and  a  very  closely 
balanced  alloy  to  shrink  first  and  then 
expand.     Obviously  this  is  because  there 


Figure  39  —  Diagram  showing  mercury 
gradient  in  a  partially  dissolved  alloy 
granule. 

is  sufficient  mercury  present  to  produce 
the  maximum  action  possible  from  the 
metals,  while  if  the  mercury  is  limited,  it 
can  only  produce  action  on  the  amount  of 
alloy  dissolved  and  must  then  cease.  To 
avoid  this  sloppy  excess  of  mercury,  which 
not  only  produces  excessive  movement, 
but  weakens  the  amalgam,  both  alloy  and 
mercury  should  be  weighed  with  a  reason- 
ably accurate  balance.  Weighing  will 
prove  a  decided  economy  as  one  soon 
acquires  the  ability  to  judge  the  approxi- 
mate amount  required  for  cavities  of 
various  sizes,  while  it  is  impossible  to 
guess  the  amount  when  pouring  the 
materials  from  a  container.  We  should 
plan  to  have  plenty  of  amalgam  for  each 
filling,  without  repeating  the  mix,  but  it 
is  useless  extravagance,  especially  in  the 


case  of  large  fillings,   to  amalgamate  two 
or  three  times  the  required  amount. 

Sufficient  mercury  should  be  used  to 
produce  an  amalgam  of  such  consistency 
that  fluid  mercury  will  appear  on  the  sur- 
face of  the  mass,  while  it  is  being  rapidly 
rolled  in  the  palm.  The  manufacturer 
should  determine  the  ratio  of  mercury 
which  will  produce  this  consistency  for 
each  lot  of  alloy,  as  the  dentist  can  only 
estimate  unless  he  uses  the  micro-microm- 
eter and  dynamometer,  and  spends  con- 
siderable time.  It  is  necessary  to  determine 
the  ratio  for  each  lot  of  alloy,  as  it  is  im- 
practicable to  make  all  batches  of  alloy  so 
that  the  proportion  of  mercury  required 
will  be  the  same.  For  this  reason,  we 
should  pay  no  attention  to  the  directions 
for  the  ratio  of  mercury  if  the  same  direc- 
tions are  used  with  every  batch  of  alloy. 

There  should  always  be  a  slight  excess 
of  mercury,  to  make  the  best  amalgam, 
but  this  excess  should  be  expelled  as  manip- 
ulation progresses. 

THE  MORTAR  AND  PESTLE 

Many  methods  of  amalgamating  alloy 
and  mercury  have  been  advocated,  and  all, 
perhaps,  have  some  advantages  for  certain 
varieties  of  alloy.  The  accurately  balanced 
dental  amalgam  alloys  have  proved  most 
successful  when  triturated  in  the  wedg- 
wood  mortar.  One  of  these  will  be  found 
in  nearly  every  dental  office,  but  the  pestle 
which  accompanies  it  is  usually  worse  than 
useless  because  of  its  shape  and  size.  The 
pestle  should  be  so  shaped  that  it  will  fit 
into  the  contour  of  the  mortar  and  large 
enough  to  cover  most  of  the  floor,  so  that 
as  much  as  possible  of  the  alloy  will  be 
worked  continuously.  The  handle  of  the 
pestle  should  be  generous  in  size  to  permit 


38 


AMALGAMATION   OF 


ALLOY   AND 


MERCURY 


a  firm  grasp.    A  pestle  wliich  is  correct  in 
form  is  shown  in  Figure  40. 

The  roughness  and  porosity  of  the  new 
wedgwoocl  will  prove  to  be  a  source  of 
considerable  annoj^ance  at  first,  as  the 
amalgam  will  adhere  to  the  mortar  and  is 
difficult  to  remove.  The  deeper  pores  will 
become  filled  with  the  amalgam,  in  time, 
and  the  trouble  will  then  cease.  It  will 
hasten  matters  to  grind  the  inner  surface 


Figure  40  —  Wedgwood  mortar,  with 
large  pestle  fitting  into  the  contour  of 
the  mortar,  correct  in  form  for  triturating 
alloy  and  mercury. 

of  the  mortar  with  powdered  emery,   or 
other  suitable  abrasives,  until  it  is  smooth. 

PRECEDING  AMALGAMATION 

Before  the  amalgamation  of  the  alloy 
with  the  mercury  is  begun,  everything 
about  the  cavity  should  be  in  readiness  for 
condensation  and  the  completion  of  the 
operation.  The  instruments  for  condensing 
should  be  at  hand  and  should  be  tested  in 
the  cavity,  to  make  sure  that  they  have 
the  proper  form  to  reach  the  angles  of  the 
cavity.  There  should  be  no  delay  after  the 
alloy  and  mercury  are  amalgamated  before 
condensing  is  begun. 


AMALGAMATION 

To  amalgamate  the  alloy,  begin  with  a 
circular  motion  of  the  pestle,  using  very 
light  pressure  so  that  the  mercury  will  not 
be  forced  away  from  the  alloy.  As  soon 
as  the  alloy  has  taken  up  the  free  mercury, 
shghtly  heavier  pressure  should  be  used  on 
the  pestle,  and  this  should  be  continued 
until  all  of  the  granules  of  the  alloy  have 
been  coated  and  free  mercury  is  not 
apparent  in  the  mortar.  When  this  point 
is  reached,  the  amalgam  should  be  removed 
to  the  palm  where  it  should  be  rolled 
and  worked  rapidly.  This  rapid  rolhng 
seems  to  bring  out  the  excess  mercury 
better  than  other  methods  and  also  insures 
a  better  solution  by  rapidly  changing  the 
position  of  all  of  the  alloy  granules. 

As  the  amount  of  mercury  used  is  in- 
sufficient to  form  a  chemical  combination 
with  the  metals  of  the  alloy,  the  particles 
of  alloy  are  onlj'  partially  dissolved  and 
a  uniting  envelope  of  amalgam  is  formed, 
lea\'ing  an  undissolved  integral  granule 
which  assists  in  retaining  the  original 
strength  of  the  alloy. 

A  series  of  dynamometer  tests  made  to 
determine  the  comparative  effect  of  partial 
and  thorough  amalgamation  upon  the 
strength  of  amalgam  resulted  as  follows: 

ALLOY  No.   178 

Alloy  eight  parts  —  Mercury  ten  parts. 

Ground  with  mortar  and  pestle  ^4  minute.  In 
palm  3I4  minutes.    Total  4  minutes. 

Granules  well  dissolved  in  mercury.  All  excess 
mercury  removed. 

Heavy  mallet  force  for  condensation. 

Average  crushing  strength  test  over  a  period 
of  2^2  months,  375  pounds. 

ALLOY  No.   178 

Alloy  and  Mercury  equal  parts. 

Ground  with  mortar  and  pestle  -2  minute.  In 
palm  52  minute.    Total  1  minute. 

Granules  weU  coated  but  not  dissolved  in 
mercury.    All  excess  mercury  removed. 

Heavy  mallet  force  for  condensation. 

Average  crushing  strength  test  over  period  of 
2  months,  464  potmds. 


[39] 


STANDARDIZING 


THE         AMALGAM         FILLING 


THE  AMALGAM  DYNAMOMETER 

The  dynamometer  used  for  this  and  other 
tests  of  the  compressive  strength  of  amal- 
gam, described  in  this  article,  is  shown  at 
Figure  41.  Cubes  of  amalgam  .085  inch 
are  made  in  the  block  shown  in  the  lower 


that  amalgam  is  but  slightly  ductile  and 
that  the  full  force  of  occlusion  is  often 
exerted  upon  frail  margins,  which  are 
tested  to  their  utmost  to  resist  fracture. 
Not  only  this,  but  as  the  strength  of 
amalgam  is  increased,  the  tendency  to  flow 


Figure  41  —  Amalgam  Dynamometer  used  for  measuring  the 
compressive  strength  of  amalgam. 


part  of  the  illustration;  these  are  placed 
in  the  steel  jaws  of  the  instrument  and  a 
compressive  force  is  applied,  by  means  of 
the  screw  head  at  the  right.  As  the  pres- 
sure is  increased,  the  dial  registers  the 
pressure  in  pounds;  when  the  amalgam  is 
crushed,  one  hand  of  the  dial  remains 
stationary,  registering  the  exact  amount  of 
force  which  has  been  required  to  crush 
the  amalgam.  A  good  amalgam  resists 
a  pressure  of  from  350  to  600  pounds; 
many  amalgams  are  fractured  before  the 
pressure  reaches  200  pounds. 

It  must  be  borne  in  mind  that  these 
tests  are  made  with  very  small  fillings, 
.085  inch,  with  fillings  of  ordinary  size  the 
strength  would  be  increased  proportion- 
ately. It  is  evident  that  this  large  factor 
of  safety  is  necessary  when  one  considers 


is  diminished.  It  is  as  important  that 
amalgam  should  resist  flow  as  that  it 
should  resist  fracture.  The  leaking  margins 
that  we  so  frequently  observe  are  more 
often  from  flow  than  from  shrinkage. 
Flow  of  amalgam  is  its  tendency  to  move 
under  pressure,  either  sustained  or  inter- 
mittent; it  is  only  a  change  of  form  and 
not,  in  any  way,  an  increase  in  the  bulk 
of  the  filling,  hence,  if  the  filling  moves  in 
the  cavity  in  the  least  degree,  a  leak  must 
be  created  at  some  point. 

Tests  of  amalgam  for  flow  are  also  made 
with  the  dynamometer.  Cubes  of  amalgam 
of  the  same  size  as  those  used  for  measuring 
strength,  .085  inch,  are  placed  in  the  jaws 
of  the  dynamometer  and  pressure  is 
applied  until  the  dial  registers  one  hundred 
pounds.  The  small  micrometer  dial,  at 
the  right  of  the  large  dial,  is  set  at  zero. 


[40] 


AMALGAMATION 


O  F 


ALLOY 


AND 


MERCURY 


As  the  amalgam  is  compressed  the  microm- 
eter dial  registers  the  amount  of  com- 
pression. 

EXPRESSING  EXCESS  MERCURY 

The  excess  mercury,  necessary  for  amal- 
gamation, should  be  removed  from  the 
amalgam  by  expressing  it  through  muslin 
with  flat  nosed  pliers.  In  experiments  with 
annealed  alloys  we  have  found  that  a  lesser 
amount  of  pressure  applied  through  an 
interval  of  time  will  remove  more  mercury 
than  a  greater  amount  of  pressure  applied 
and  immediately  removed. 

It  is  difficult  to  state  the  exact  con- 
sistency at  which  amalgam  should  be  placed 
in  the  cavity.  The  most  desirable  consist- 
ency is  that  obtained  by  expressing  all 
of  the  mercury  in  excess  of  the  amount 
required  for  perfect  adaptation,  as  the 
greatest  strength  in  the  amalgam  is  secured 
by  bringing  the  undissolved  particles  of 
alloy  as  closely  together  as  possible.  Unless 
the  operator  realizes  clearly  how  very 
difficult  it  is  to  adapt  amalgam  thoroughly, 
he  should  experiment  on  cavities  in  ex- 
tracted teeth,  under  conditions  as  nearly 
normal  as  possible,  splitting  the  teeth  and 
examining  the  adaptation  with  a  magni- 
fying glass  after  the  filling  has  thoroughly 
set.  Possibly  a  magnifying  glass  will  not 
be  necessary.  Because  of  this  difficulty  of 
adaptation  and  because  amalgam  with  all 
the    excess    mercury    removed    sets    very 


rapidly,  it  is  very  rarely  advisable  to  begin 
condensing  with  amalgam  as  dry  as  it  is 
possible  to  make  it. 

MIXING  SOLUTIONS 

Amalgam  should  be  kept  free  from  water, 
saliva,  and  chemical  solutions,  during  its 
manipulation,  as  any  moisture  which 
comes  in  contact  with  it  tends  to  decrease 
its  strength  about  one-third.  There  are 
on  the  market  a  variety  of  solutions  for 
"washing  alloys,  to  make  them  white  and 
aid  amalgamation."  These  solutions  may 
possibly  remove  tarnish  from  some  alloys, 
but  this  does  not  make  the  filling  any 
whiter.  Their  principal  harm  lies  in 
moistening  the  granules  and  preventing 
amalgamation.  The  effect  of  a  two  per 
cent  HCl  solution  when  used  for  this 
purpose  is  shown  by  the  following  result 
of  tests  made  with  the  dynamometer: 

ALLOY  No.  10 

Alloy  five  parts  —  Mercury  six  parts. 

2%  HCl  mixing  solution  used. 

Amalgam  packed  with  heavy  hand  pressure. 

Average  crushing  strength,  283  pounds. 

ALLOY  No.  10 

Alloy  five  parts  —  Mercury  six  parts. 

No  mixing  solution  used. 

Amalgam  packed  with  heavy  hand  pressure. 

Average  crushing  strength,  389  pounds. 

Other  tests  show  that  alcohol,  water,  or 
saliva,  coming  in  contact  with  the  alloy 
before  amalgamating,  have  a  similar  effect. 


Section  IV.    Instrumentation  and  Condensation 


HAVING  made  all  preparation  possible 
for  the  completion  of  the  operation 
before  amalgamating  the  alloy  and  mer- 
cury, we  should  begin  to  place  the  amalgam 
in  the  cavity  and  condense  it  immediately 


after  the  excess  mercury  is  expressed  from 
the  amalgam. 

To  secure  the  greatest  strength  in  the 
amalgam,  we  must  express  a  still  further 
amount  of  excess  mercury  while  condensing 


[41] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


and  bring  the  undissolved  portions  of  the 
alloy  granules  as  closely  together  as  pos- 
sible. This  is  best  accomplished  by  the 
use  of  properly  shaped  condensing  instru- 
ments with  the  hand  mallet.  The  hand 
mallet  not  only  supplies  the  stress  necessary 


Figure  42  —  Photomicrograph  of  dental 
amalgam,  showing  accidental  voids  result- 
ing from  insufficient  condensation. 

to  condense  the  mass  but,  in  addition, 
agitates  and  vibrates  the  alloy  granules, 
reducing  the  void  volume  and  bringing  to 
the  surface  further  excess  of  mercury 
which  may  then  be  removed.  Dr.  Black 
found  that  the  average  amalgam  filling 
contained  about  fourteen  per  cent  of  air 
space.  It  is  unnecessary  to  say  that  these 
air  spaces  or  voids  are  not  desirable. 

ACCIDENTAL  AND  INHERENT  VOIDS 
Voids  are  of  two  kinds,  accidental  and 
inherent.  Accidental  voids,  which  are 
much  the  larger,  result  from  insufficient 
condensation.  They  may  and  should  be 
minimized  by  proper  condensing,  with 
heavy  pressure.  Inherent  voids  are  due 
to  the  diffusion  of  excess  mercury  from  the 
mercury-rich  portion  of  the  alloy  into  the 
alloy-rich  portion.     The  black  areas  seen 


in  Figure  42  are  accidental  voids  in  a 
mercury-rich  amalgam,  poorly  condensed. 
Figure  43  shows  the  same  amalgam  thor- 
oughly condensed  and  containing  a  smaller 
proportion  of  mercury.  The  alloy-rich 
portion  of  the  amalgam  appears  as  large 
white  grains,  the  small  dark  areas  are 
almost  entirely  inherent  voids.  Amalgam 
of  this  structure  possesses  the  highest 
crushing  strength  and  the  minimum  volume 
change.  It  is  the  structure  which  should 
be  attained  in  amalgam  restorations,  as 
determined  by  physical  tests,  metallo- 
graphic  investigation,  and  actual  clinical 
observation. 

THE  RELATION  OF  VOIDS  TO  VOLUME 
CHANGES 

We  find  that  the  phenomena  accompany- 
ing voids  throw  some  light  on  the  volume 
changes   of  amalgam.     An   observed  fact 


^n^^^ 

^^H 

Figure  43  —  Photomicrograph  of  dental 
amalgam  with  smaller  inherent  voids, 
resulting  from  the  diffusion  of  mercury 
into  the  alloy  granules. 

is  that  with  excess  mercury  a  tin-rich  alloy 
shrinks  more  and  a  silver-rich  alloy  expands 
more  than  normally  is  the  case.  As  pre- 
viously noted  tin  forms  a  shrinking  solid 


[42] 


PROPER 


CONDENSATION 


O    F 


AMALGAM 


solution  with  mercury,  and  silver  an  expand- 
ing one.  When  an  excess  of  mercury 
is  used,  it  finally  becomes  effective  in  form- 
ing more  tin-rich  amalgam,  accompanied 
by  increased  shrinkage;  contrarily,  more 
silver-rich  amalgam  is  accompanied  by 
increased  expansion. 

A  secondary  phenomenon  causing  ex- 
pansion in  the  silver-rich  amalgam  arises 
from  the  fact  that  the  particles  grow  in 
diameter  as  the  envelope  of  amalgam  in- 
creases in  thickness  and  the  interstitial 
adhering  mercury  diffuses  toward  the 
center,  leaving  inherent  voids.  On  the 
other  hand,  tin  simply  melts  in  mercury 
without  formation  of  particles  of  larger 
diameter  and  voids.  The  explanation  of 
this  behavior  involves  a  discussion  of 
molecular  physics  and  physical  chemistry 
which  will  be  considered  in  a  later  publi- 
cation. 

BEGINNING  CONDENSING 

In  placing  the  amalgam,  it  is  often 
advisable  to  begin  with  a  small  piece  that 
is  not  as  dry  as  the  remainder  of  the  mix. 
It  can  be  condensed  and  adapted  more  per- 
fectly than  the  very  dry  amalgam  and  the 
excess  mercury  can  be  removed  from  it, 
as  it  makes  its  appearance,  during  the 
condensing.  Instruments  which  will  carry 
the  amalgam  into  the  angles  and  over  the 
margins  of  the  cavity,  as  shown  in  Figure 
44,  should  be  used  to  begin  condensing. 
Force  should  be  applied  first  in  the  angles 
of  the  cavity,  then  the  condenser  should 
be  stepped  so  as  to  reach  the  margins  last. 

HEAVIER  PRESSURE 

After  the  base  of  the  cavity  is  covered, 
larger  pieces  of  amalgam  and  larger  con- 
densing instruments  may  be  used,  as  the 
size  of  the  cavity  will  permit,  and  the  force 
may  be  greatly  increased  as  the  size  of  the 


condensers  and  the  density  of  the  amalgam 
increase.  This  stage  of  the  operation  is 
shown  in  Figure  45. 

ADVANTAGES  OF  HEAVY  CONDENSING 

Amalgam  is  treacherous  in  that  it  readily 
gives  the  appearance,  on  the  surface,  of 
thorough  condensation,  and  only  careful 
examination  will  reveal  the  defects  caused 
by  a  failure  to  thoroughly  seat  and  con- 
dense it.  One  of  the  advantages  of  con- 
densing it  to  the  density  described  is  that 
this  may  compress  the  dentin  walls,  that 


Figure  44  —  Beginning  condensation  with 
a  small  instrument,  condensing  into  the 
angles  and  margins  of  the  cavity. 

is  it  may  spring  them  apart  so  that  their 
elasticity  will  produce  a  continued  force 
upon  the  amalgam,  an  effect  similar  to  the 
advantage  gained  by  the  use  of  gold  foil. 
This  continued  force  exerted  by  the  com- 
pressed walls  will,  to  an  extent,  overcome 
the  disadvantage  of  any  minute  volume 
changes  occurring  in  the  bulk  of  the  resto- 
ration and  will  produce  a  contact  of  the 
filling  with  the  cavity  walls  which  is  proof 
against  leakage. 


[43] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


CONDENSING  OVER  ALL  MARGINS 
SIMULTANEOUSLY 

The  excess  of  mercury  which  will  come 
to  the  surface  as  a  result  of  the  heavy  force 
used  in  condensing  should  be  removed 
with  suitable  instruments  and  drier  amal- 
gam should  be  added.     Finally,  to  fill  the 


Figure  45  —  The  use  of  a  condenser  as 
large  as  the  cavity  will  permit. 

cavity,  a  large  excess  of  amalgam  should 
be  added  and  a  condensing  instrument, 
sufficiently  large  to  cover  all  of  the  margins 
simultaneously,  should  be  used,  with  the 
hand  mallet,  to  drive  the  amalgam  tight 
on  all  margins.  This  simultaneous  pres- 
sure over  all  of  the  margins  is  necessary  as 
on  account  of  the  semi-plastic  nature  of 
amalgam  it  would  be  impossible  to  make  a 
wide  area  of  margins  tight  by  passing  from 
one  point  to  another.  Naturally  pressure 
down  at  one  point  will  produce  pressure 
up  at  another  point  and  a  leak  will  result. 
The  large  excess  of  amalgam  used  has  the 
advantage  of  absorbing  any  excess  of 
mercury  from  the  cavity  margins  and  gives 


strength  at  this  point,  where  strength  is 
most  essential ;  it  also  protects  the  margins 
from  the  blows  of  the  condenser  and  makes 
possible  closer  adaptation  to  the  cavity 
walls  and  margins. 

Figure  46  shows  the  use  of  a  large  con- 
densing instrument  which  produces  pres- 
sure over  all  the  margins  simultaneously. 

EFFECT  OF  HEAVY  CONDENSING 

To  determine  the  comparative  strength 
of  amalgam  from  which  the  excess  mercury 
has  been  removed  and  which  has  been 
thoroughly  condensed  by  the  method  out- 
lined here,  the  following  tests  were  made: 
Fifty  fillings,  .085  inch  cube,  were  made  in 
steel  dies,  all  from  the  same  alloy.  Twenty- 
five  had  the  excess  mercury  removed  by 
placing  the  amalgam  in  a  small  piece  of 
muslin  and  expressing  it  with  flat-nosed 
pliers  and  were  thoroughly  condensed  by 
mallet  force.  Twenty-five  were  made  by 
expressing  the  mercury  between  the  thumb 
and  fingers  and  were  condensed  as  thor- 
oughly as  possible  by  hand  pressure.  At 
varying  intervals  the  same  number  of 
fillings  from  each  lot  were  crushed  in  the 
dynamometer  and  a  record  was  made  of 
the  crushing  strength.  The  average  strength 
of  those  which  had  been  thoroughly  con- 
densed by  mallet  force,  after  removing  the 
excess  mercury  through  muslin  with  pliers, 
was  514  pounds;  of  those  with  the  usual 
amount  of  mercury  remaining  and  con- 
densed by  hand  pressure,  385  pounds,  that 
is,  129  pounds  or  dS}4  per  cent  in  favor  of 
mallet  condensing  and  a  minimum  of 
mercury. 

CORROBORATIVE  TESTS 

A  series  of  tests  made  recently  by  Dr. 
H.  A.  Merchant  confirms  the  result  of 
previous  tests  of  methods  of  manipulation 
and  condensation  and  also  shows  the  effect 


[44] 


EFFECT 


O   F 


UNDUE 


EXCESS        OF        MERCURY 


of  heat  upon  amalgams  manipulated  and 
condensed  in  various  ways. 

The  object  of  the  heat  treatment  is  to 
produce  an  amalgam  of  the  same  structure 
that  occurs  in  fillings  subjected  to  changes 
of  temperature  from  hot  food  and  drinks. 
It  may  be  objected  that  150°  F.  is  the 
maximum  temperature  experienced  in  the 
mouth;  however,  the  same  effect  occurs  at 
lower  temperature  but  requires  a  longer 
period  of  time.  The  maximum  tempera- 
ture was  chosen  merely  to  obviate  unneces- 
sary delay.  Dr.  Merchant's  findings  are 
tabulated  on  page  46.  Some  of  the  more 
important  are  noted  following: 

TESTS    OF   A  BALANCED    NON-ZINC   ALLOY 

Test  No.  1  was  made  with  a  non-zinc 
alloy  of  80  mesh  filings.  The  alloy  and 
mercury  received  only  light  initial  trit- 
uration. With  mallet  force  for  condens- 
ing, the  small  granules  were  driven  to- 
gether so  that  the  excess  mercury  was 
largely  driven  off.  As  little  of  this  mercury 
was  absorbed  by  the  alloy,  the  resulting 
amalgam  was  silver-rich.  The  loss  of 
strength  resulting  from  heat  treatment  was 
small. 

Test  No.  2.  The  only  variation  from 
test  No.  1  was  the  use  of  pressure  for 
grinding  the  alloy  with  mercury  so  that 
the  granules  were  partly  crushed.  This 
cold  work  partially  unaged  the  alloy,  so 
that  it  retained  more  mercury  than  in  test 
No.  1.  The  effect  of  this  higher  percent- 
age of  mercury  is  graphically  shown  in  the 
resulting  loss  of  one-half  the  strength  of 
the  amalgam  under  heat  treatment. 

Test  No.  3.  In  this  test  the  same  alloy 
was  used  as  in  test  No.  1  and  No.  2.  The 
object  of  this  test  was  to  learn  the  effect 
of  large  percentages  of  mercury  such  as 
have  been  advocated,  recently,  by  a  num- 


ber of  prominent  dentists  for  the  purpose 
of  making  air-tight  fillings  in  steel  tubes. 
Amalgam  of  this  strength  would  flow  and 
leave  a  crevice  about  the  margins  of  a 
tooth  which  would  soon  defeat  the  object 
of  the  operation.  The  fallacy  of  a  mercury- 
rich  amalgam  is  evident  when  its  weakness 
is  considered. 

Tests  Nos.  4  and  5  show  the  volume 
change  of  a  non-zinc  alloy,  due  to  heat 
treatment.  It  will  be  noted  that  heat 
produced  practically  no  change  in  the 
volume  of  amalgam  when  the  parts  of 
mercury  were  only  slightly  in  excess  of  the 
parts  of  alloy.     However,  in  test  No.   5 


Figure  46  —  Condensing  a  large  excess  of 
amalgam  over  all  the  margins  of  the 
cavity,  by  the  use  of  a  large  condenser 
which  win  cover  all  the  margins  simultane- 
ously. 

where  the  percentage  of  mercury  is  too 
high,  the  sloppy  amalgam  resulting  suffers 
great  volume  change.  This  effect  should 
be  borne  in  mind  by  those  inclined  to  use 
amalgam  in  a  sloppy  condition. 


N 


STANDARDIZING        THE         AMALGAM         FILLING 


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46 


EFFECT 


O   F 


HEAT 


UPON 


ZINC 


ALLOY 


TESTS  OF  A  BALANCED  ZINC  ALLOY 

Tests  Nos.  6  to  9  were  made  with  a 
balanced  zinc  alloy,  containing  5  per  cent 
of  copper.  Test  No.  6  shows  the  decided 
loss  of  strength  resulting  from  the  zinc 
content  and  the  large  proportion  of  mer- 


cury required  for  this  alloy.  Tests  Nos.  8 
and  9  show  the  effect  of  heat  treatment 
upon  this  shrinking  amalgam,  the  excess 
of  mercury  used  causing  excessive  move- 
ment in  the  direction  of  the  balance  of 
the  alloy. 


Section  V.    Contour  and  Finish  of  the  Restoration 


AFTER  the  amalgam  has  been  con- 
-  densed  it  should  not  be  disturbed 
until  it  has  crystallized  sufficiently  so  that 
it  can  be  carved.  If  the  condensing  has 
been  thoroughly  done,  as  described,  crys- 
tallization will  usually  take  place  in  a  very 
few  minutes.  The  carving  should  be  begun 
as  soon  as  the  density  of  the  mass  will  per- 
mit, always  before  the  amalgam  has  set. 

CARVING  THE  OCCLUSAL  FORM 

It  is  of  the  greatest  importance  to  the 
function  of  mastication  that  the  occlusal 
form  of  the  tooth  should  be  accurately 
restored.  Flat  or  curved  surfaces  do  not 
permit  the  holding  or  tearing  of  foods; 
the  occlusal  surfaces  must  have  their  proper 
form  of  cusps,  sulci,  pits,  and  occlusal 
planes,  otherwise  the  masticating  surface, 
as  a  unit,  will  soon  form  the  habit  of 
shifting  the  burden  of  mastication  to  those 
surfaces  which  more  properly  function. 
A  comparison  of  the  smooth,  polished  sur- 
faces, shown  at  C  in  Figure  47,  with  the 
carved  surfaces  of  A  and  B  will  show  at 
once  the  superiority  of  the  latter  in  grasping 
and  tearing  food. 

The  restoration  of  the  occlusal  surface 
to  nature's  form,  so  that  it  will  work  in 
harmony  with  the  antagonizing  teeth, 
is  an  especial  advantage  in  the  case  of 
extensive  restorations  or  amalgam  crowns. 
Before  beginning  to  carve  these  restorations 


the  matrix  should  be  ground  with  a  stone 
in  the  engine  handpiece  until  it  does  not 
interfere  with  the  occlusion  or  with  the 
carving.  The  excess  of  amalgam  should 
be  carved,  or  ground  down,  and  the  occlu- 
sion tested,  before  the  amalgam  has 
thoroughly  hardened. 

As  rotary  instruments  cut  only  concave 
surfaces  and  the  cusp  surfaces  are  mostly 
convex,  we  find  little  use  for  engine  driven 
instruments,  for  this  purpose,  except  for 
removing  large  excesses  of  amalgam  and 


Figure  47 — At  A  and  B  are  amalgam  res- 
torations carved  to  the  correct  occlusal 
form.  Their  superiority  over  the  smoothly 
finished  surface  at  C,  for  holding  and 
tearing  food,  is  readily  apparent. 

approaching  the  general  form  of  the  tooth. 
The  carving  which  differentiates  the  res- 
toration from  the  filling  can  be  done  cor- 
rectly only  with  hand-carving  instruments. 


[47] 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


As  the  carving  proceeds  it  should  be 
tested  frequently  until  it  is  correct.  A 
high  degree  of  art  may  be  attained  in  this 
work  by  studying  the  natural  tooth  forms 
and  practicing  their  reproduction.  As  it 
is  impossible  to  smooth  these  carved  sur- 


Figure    48 
tearing. 


Removing    the    matrix    by 


faces  with  disks  and  the  mandrel,  they 
should  be  smoothed,  as  soon  as  they  are 
carved,  with  pumice  carried  on  pointed 
tooth  polishing  brushes. 


and  remove  it.    The  other  section  may  be 
removed  readily. 

The  seamless  band  matrix,  used  for 
extensive  or  complete  restorations,  is 
removed  by  cutting  through  the  buccal 
surface  with  a  sharp  instrument  or  stone, 
as  in  Figure  49,  and  tearing  the  band  out 
in  sections.  This  should  rarely  be  done 
before  the  amalgam  has  thoroughly  set, 
never  in  less  than  twenty-four  hours. 

The  necessary  carving  having  been  done, 
the  excess  of  amalgam  removed,  and  the 
filling  given  the  correct  form,  the  patient 
should  be  dismissed  with  an  appointment 
for  the  final  finishing  of  the  restoration. 

Many  dentists  complain  that  patients 
will  not  return  for  this  final  finishing,  this 
is  usually  because  they  do  not  understand 
that  it  is  essential.  They  should  be  told 
that  the  operation  is  not  complete  and 
that  they  must  return. 

THE  FINAL  POLISHING 

The  finishing  and  polishing  of  an  amal- 
gam restoration  is  accomplished  in  the 
same  manner  as  the  finishing  and  polishing 
of  a  gold  foil  restoration.  The  proximal 
surface  from  the  point  of  contact  to  the 


REMOVING  THE  MATRIX 

When  the  tied  copper  matrix  has  been 
used,  it  may  be  removed  at  this  point,  if 
the  restoration  is  not  extensive.  The 
ligature  should  first  be  cut  and  removed, 
then  with  a  sharp  pointed  instrument 
finish  cutting  the  slit  in  the  matrix  from 
the  contact  to  the  occlusal  edge,  to  further 
weaken  it.  With  pliers,  or  the  fingers, 
grasp  one  end  of  the  matrix,  while  holding 
the  other  end  firmly  against  the  tooth,  tear 
it  with  a  twisting  motion  from  the  contact 
to  the  gingival,   as  shown  in  Figure  48, 


Figure  49  —  Seamless  band  matrix  with 
slits  ready  for  removal. 


48 


FINAL        FINISHING        OF        THE        RESTORATION 


gingival  margin  should  be  finished  with 
knives,  files,  and  strips.  Disks  and  stones 
are  useful  upon  the  other  surfaces,  but  a 
disk  should  never  be  allowed  to  pass  over 
the  contact  point  and  flatten  it.  The 
point  of  contact  should  not  be  a  surface 
contact,  but  should  be  gently  rounded,  so 
that  food  will  pass  through  the  embrasure 
and  be  freed  readily,  yet  not  so  reduced 


that  food  will  pass  over  it.  If  the  occlusal 
surface  has  been  carefully  smoothed  with 
brush  wheel  and  pumice,  directly  after 
carving,  there  will  be  no  trouble  in  obtain- 
ing a  good  final  finish  with  the  brush  wheel 
and  chalk,  after  the  amalgam  has  set.  For 
the  final  finish  of  the  other  surfaces  buff 
wheels  and  brush  wheels,  carrying  chalk 
and  other  fine  abrasives  should  be  used. 


Section  VI.    Profitable  Fees  for  Amalgam  Restorations 


THE  amalgam  operation  which  we  have 
outlined  is  not  a  cheap  operation  and 
should  not  be  considered  by  the  patient 
as  a  cheaper  substitute  for  a  gold  crown  or 
other  work  which  usually  brings  a  better 
remuneration. 

The  question  of  adequate  compensation 
for  amalgam  work  is,  perhaps,  one  of  the 
most  vital  ones  confronting  the  dentist 
today.  When  it  is  considered  that  from 
fifty  to  seventy-five  per  cent  of  all  dental 
operations  are  amalgam  operations,  its 
importance  is  at  once  apparent.  As  with 
most  situations  in  need  of  betterment,  the 
remedy  probably  lies  not  in  some  sweeping 
and  miraculous  change  to  be  brought  about 
at  once,  but  in  a  gradual  improvement 
brought  about  through  various  influences. 

The  dentist  should  have  a  more  thorough 
realization  of  the  importance  of  restoring 
even  an  ordinary  pit  or  flssure  cavity  to 
correct  anatomical  form.  He  needs  to 
realize  that  the  cost  of  the  amalgam  alloy 
he  uses  is  almost  a  negligible  factor  in  the 
cost,  to  him,  of  the  completed  operation. 
He  should  know  and  constantly  impress 
upon  his  patients  that  the  value  of  his 
services  to  them  lies  not  in  the  use  of 
porcelain  rather  than  gold,  or  of  gold 
rather  than  plastic  materials,  but  in  the 
restoration  of  a  diseased  member  to  its 


M 


proper  form  and  function  in  the  mouth, 
and  in  the  permanence  of  the  operation. 

EDUCATING  THE  PATIENT 

There  are  many  patients  with  ill  fitting 
gold  crowns,  with  extensive  amalgam 
fillings,  overhanging  at  the  gingival  margin, 
with  contact  points  improperly  shaped,  or 
lacking,  who  believe  that  the  consequent 
loss  of  tissue  and  the  constant  discomfort 
of  food  retained  between  such  teeth,  is  a 
necessary  result  of  a  dental  operation. 
There  are  others  who  think  that  an  amal- 
gam filling  must  shrink  and  will  need  to  be 
replaced  in  a  year  or  two  at  most;  that  it 
will  necessarily  blacken  and  discolor  the 
tooth. 

The  dentist  is  the  patient's  only  authori- 
tative source  of  information  on  dental 
subjects;  a  careful  and  simply  worded 
explanation  of  his  dental  needs,  and  of  the 
care  and  time  necessary  to  produce  a  result 
which  will  conserve  his  health,  rather  than 
help  to  undermine  it,  should  gain  his 
complete  co-operation  and  should  convince 
him  that  the  operation  is  sufficiently  im- 
portant to  command  an  adequate  fee. 

DEMONSTRATION 

When  necessary,  illustrations,  a  tj^podont 
with  fillings,  or  carved  plaster  models  may 
be    shown    to    demonstrate    the    correct 


STANDARDIZING 


THE 


AMALGAM 


FILLING 


restoration,  in  comparison  with  the  gold 
crown  or  the  amalgam  filling  which  lacks 
contour   antl    occlusal   form. 

ADVANTAGES  OF  THE  AMALGAM 
RESTORATION 

Patients  are  willing  to  pay  an  adeciuate 

fee  for  good   dentistry.      When  they  are 

made  to  understand  that  thej^  are  getting 


\^K 


Figure  50  —  Recurrence  of  decay  due  to 
movement  of  the  amalgam,  from  the 
use  of  unbalanced  alloys,  to  improper 
cavity  preparation,  lack  of  matrix,  in- 
sufficient condensation,  and  lack  of 
adaptation.  None  of  these  fillings  show 
proper  contour,  occlusal  form,  or  contact. 

value  commensurate  with  the  amount  paid, 
there  will  be  ver}"  little  objection  to  reason- 
able fees.  The  advantages  of  the  operation 
should  be  carefully  elucidated,  especiall}^ 
in  cases  where  large  amalgam  restorations 
are  needed. 

Explain  that  the  contour  of  the  enamel 
at  the  gingival  margin  does  not  need  to  be 
destroyed,  as  it  must  be  if  the  tooth  is 
crowned;  that  the  adaptation  of  the 
margins  is  so  perfect  that  micro-organisms 
can  not  enter  the  tooth  and  cause  recur- 
rence of  decay;  that  there  are  no  rough 


margins  to  irritate  the  soft  tissues  and  set 
up  inflammation,  which  is  often  followed 
by  most  serious  results;  that  the  whole 
restoration  is  solid  metal,  it  can  not  wear 
out.  it  will  not  absorb  foul  liquids  as  a 
mass  of  cement,  such  as  a  crown  contains, 
will  always  do;  that  the  restoration  re- 
quires as  much  time  and  skill  as  a  crown 
does;  that  the  material  is  the  best  of  its 
kind  and  that  the  operation  will  perma- 
nently restore  the  occlusal  form  and  masti- 
cating function  of  the  tooth. 

Nothing  which  has  been  said  here,  how- 
ever, should  be  taken  to  countenance  an 
advance  in  fees  which  is  not  justified  by  the 
service  rendered.  There  is  no  value  in- 
herent in  a  higher  priced  alloy  which 
justifies  the  increase  of  fees  if  the  quality 
of  the  result  is  not,  at  the  same  time, 
advanced  commensurately.  An  alloy  made 
to  render  the  highest  service  may  be 
misused  by  improper  amalgamation,  by 
undue  excesses  of  mercury,  by  insufficient 
condensing,  and  ma}^  be  placed  in  a  cavity 
so  poorly  prepared  that  the  result  is  of 
very  little  final  value  to  the  patient. 

Amalgam  work  like  that  shown  in  Figure 
.50,  with  recurrence  of  decay  due  to  im- 
proper cavity  preparation;  want  of  the 
matrix;  improper  condensing;  lack  of  con- 
tact, proper  contour,  and  occlusal  form; 
and  showing  movement  due  to  the  use  of 
unbalanced  alloys,  is  overpaid  at  any  price. 

"When  a  careful  technic  is  followed 
throughout  the  operation,  however,  and  an 
alloy  made  and  tested  by  scientific  methods 
is  used,  the  resulting  amalgam  restoration 
should  give  better  service  than  the  average 
inlay,  or  a  gold  foil  restoration  such  as  can 
be  made  by  the  operator  of  average  ability, 
and  the  service  rendered  should  be  the 
final  consideration  in  determining  the 
amount  of  the  fee. 


50 


Making  a  Standardized  Dental  Amalgam  Alloy 


by 

Albert  Sellner,  Chief  Chemist  of 
The  Cleveland  Dental  Mfg.  Co. 


METALLOGRAPHY  is  placed  at 
the  head  of  testing  and  investi- 
gating methods  by  the  largest 
manufacturers  of  metal  products  because 
the  physical  properties  of  metals  and  alloys, 


sition  of  a  dental  amalgam  alloy,  the  deter- 
mination of  some  of  its  physical  properties 
is  much  more  important.  For  instance: 
Is  it  a  solid  solution  or  eutectic?  Is  it 
homogenized   or   heterogeneous?      Was   it 


to  which  they  owe  their  definite  industrial     annealed    properly    and    understandingly, 


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Figure  51  —  Mr.  Sellner  weighing  the  metals  for  Crandall's 
Scientifically  Tested  Non-Zinc  Alloy. 


importance,  are  much  more  intimately 
concerned  with  proximate  composition, 
revealed  by  the  metallographic  microscope, 
than  with  ultimate  chemical  composition. 
The  application  of  metallography  to 
dental  products  possesses  novelty  and  offers 
a  considerable  advantage.  While  it  is 
necessary  to  know  the  percentage  compo- 


after  cutting,  or  merely  heated  up  blindly? 
What  structural  constituents  are  formed 
upon  its  amalgamation?  Does  its  amalgam 
shrink  or  expand,  corrode  or  waste  away, 
and  how  much?  Such  is  the  nature  of  the 
numerous  questions  which  must  be  answered. 
The  living  organism  demands  that 
modern  science  study,  with  extreme  care, 


[61] 


MAKING 


STANDARDIZED       DENTAL       AMALGAM       ALLOY 


the  metals  and  alloys  which  may  affect 
its  health  and  general  welfare.  The 
anatomy  of  a  metal  is  its  physical  and 
chemical  composition;  its  biology,  the  in- 
fluence exerted  upon  its  constitution  by 
various  treatments,  thermal  and  mechani- 


Figure  52  —  Dendritic  or  "tree"  structure 
in  a  sample  of  copper  containing  0.3  per 
cent  phosphorus.  Magnification  150X. 
Reichert  metallographic  apparatus. 

cal;  its  pathology,  the  action  of  impurities 
and  defective  treatments  upon  its  normal 
constitution.  Metallographic  dissection 
reveals  the  physical  association  of  proxi- 
mate constituents  and  features  relating  to 
desirable  or  objectionable  attributes. 

It  is  pleasing  to  know  that  the  dental 
profession  is  becoming  very  aggressive  in 
metallographic  research  as  witnessed  by 
the  papers  appearing  under  the  auspices  of 
the  National  Dental  Research  Association. 

The  preliminary  work  necessary  to  the 
production  of  a  standardized  alloy  has 
been  done  by  men  whose  devotion  to  the 
dental  profession  has  led  them  to  spend 
time  and  effort  in  making  the  investiga- 


tions which  have  been  the  foundation  for 
our  work.  Our  task  has  been  to  adapt 
their  methods  to  the  production  of  allo}- 
in  larger  quantities,  without  deviating  from 
the  scientific  methods  and  accuracy  which 
were  responsible  for  the  results  which 
they  obtained. 

An  outline  of  the  method  of  manufac- 
turing a  balanced  alloy  follows: 

Selection  of  Materials 

As  gold  has  not  proved  to  add  desirable 
qualities  to  dental  amalgam  alloys  and 
zinc  has  proved  to  be  decidedly  deleterious, 
the  onh"  metals  used  for  Crandall's  Scien- 
tifically Tested  Non-Zinc  Alloy  are  silver, 


Figure  53 — Cast  copper  with  0.1  per  cent 
oxygen.  Even  this  very  slight  impurity 
unfavorably  affects  the  physical  properties 
of  the  copper  to  such  an  extent  that  it 
should  not  be  used  for  dental  alloys. 

tin,  and  copper.  Our  problem  of  the  selec- 
tion of  materials  resolves  itself,  therefore, 
into  the  effort  to  obtain  these  three  metals 
in  the  purest  possible  state.  The  utmost 
precaution  is  taken  to  purchase  only  the 
purest  metals  obtainable  and  these  undergo 


52 


MAKING 


STANDARDIZED      DENTAL      AMALGAM      ALLOY 


further  purification  and  rigid  physical  and 
chemical  tests  in  our  laboratories.  Photo- 
micrographs of  the  structure  of  these  metals 
reveal  the  character  and  distribution  of 
impurities  and  afford  an  absolute  check  on 
claims  made  for  purity. 

It  is  a  comparatively  easy  matter  to 
obtain  silver  and  tin  of  the  necessary 
purity  for  a  balanced  alloy.  Silver  is  fur- 
nished to  us  in  the  form  of  ingots  from  the 
United  States  Assay  Office.  Our  tests  for 
fineness  must  show  999.8.  The  allowable 
impurity  for  tin  and  copper  is  0.01  per  cent. 

Copper  of  this  high  standard  of  purity 
is  obtained  with  considerably  more  diffi- 
culty than  is  the  case  with  silver  and  tin. 
Regularity  of  crystalline  structure  has  been 
pointed  out  as  the  ultimate  test  of  the 
purity  of  metals.     The  fallacy  of  this  con- 


Figure  54  —  Cast  copper  with  0.2  per  cent 
oxygen. 

tention  is  shown  by  the  following  state- 
ments summarized  from  Sauveur's  Metal- 
lography : 

Microstructure:    When   a   properly   pre- 
pared sample  of  a  pure  metal  is  examined 


under  the  microscope,  the  revealed  struc- 
ture generally  presents  the  appearance  of 
a  polygonal  network,  an  indication  that 
the  metal  is  composed  of  irregular,  poly- 
hedral grains,  each  mesh  or  polygon  of  the 
network  representing  a  section  through  a 
polyhedron. 

Idiomorphic  Crystals:   When  the  fiuidity 
of  a  substance  and  other  conditions  are 


Figure  55  —  Cast  copper  with  a  small  per- 
centage of  impurity,  causing  core  structure. 

such  that  the  formation  and  growth  of  the 
crystals  are  given  free  play,  perfect,  and 
sometimes  very  large,  crystals  are  pro- 
duced. These  perfect  crystals,  with  fault- 
less geometrical  outlines,  perfect  cubes, 
for  instance,  are  called  idiomorphic  crystals. 

Allotrimorphic  Crystals:  When  the  free 
development  of  the  crystals  is  hindered  by 
less  favorable  crystallizing  conditions  such, 
for  instance,  as  collision  or  contact  with 
other  crystals  likewise  in  the  process  of 
formation,  the  regular  external  form  is  not 
preserved  and  the  resulting  imperfect  crys- 
tals are  called  allotrimorphic  crystals,  also, 
but   more   seldom,    anhedrons   or   faceless 


[53] 


MAKING      A      STANDARDIZED       DENTAL       AMALGAM       ALLOY 


crystals.  Such  crystals  are  said  to  have 
taken  their  shape  from  their  surroundings. 
It  should  be  noted,  however,  that  allotri- 
morphic  crystals,  like  idiomorphic  crystals 
are  composed  of  crystalline  matter.  An 
allotrimorphic  crystal  may  be  regarded  as 
resulting  from  the  mutilation  of  an  idio- 
morphic crystal,  the  mutilation  affecting 
the  external  shape  only  and  not  the  crys- 
talhne  character  of  the  substance.  That  is, 
a  pure  metal  usually  exhibits  irregular  grain 
structure. 

The  tree-hke  or  dendritic  structure 
sometimes  observed  in  photomicrographs 
of  copper  has  also  been  erroneously  taken 
for  an  evidence  of  purity  of  the  metal.  It 
may  be  caused  by  0.3  per  cent  of  phos- 
phorus as  in  Figure  52. 


Figure  56  —  Electrolytic  copper. 

Ordinary  copper  may  contain  impurities 
of  lead,  antimony,  tin,  iron,  arsenic,  cuprous 
oxide  and,  in  some  instances,  zinc,  bismuth, 
sulphur,  selenium,  tellurium,  or  other 
elements  pecuhar  to  copper  from  a  certain 
district,  or  to  certain  methods  of  refining. 


In  general,  metal  dealers  are  limiting  im- 
purities to  cuprous  oxide,  arsenic,  anti- 
mony, and  bismuth.  Phosphorus  used  for 
reducing  cuprous  oxide  (2P+5Cu2O  =  P205 
+  10Cu)  slags  off  or  sublimes,  for  the  most 
part.     It   has   been   argued   that   cuprous 


Figure  57  —  Another  specimen  of  impure 
copper  containing  dendrites  or  "trees." 

oxide,  within  the  commercial  limits  of  0.4 
per  cent  to  1.2  per  cent  may  oxidize  impuri- 
ties and  permit  formation  of  copper  arsen- 
ate, bismuthate,  and  so  on,  but  we  have 
found  that  this  brittle  constituent  is  unde- 
sirable for  obvious  reasons  in  a  product 
which  must  be  balanced. 

Again  0.1  per  cent  oxygen,  meaning  0.9 
per  cent  cuprous  oxide,  forms  25.7  per 
cent  of  eutectic.  Figure  53  shows  such  a 
copper  which  is  unfit  for  use  as  its  conti- 
nuity and  desirable  physical  properties  are 
too  greatly  affected.  Small  percentages 
of  oxygen  are  hardly  accurately  determined 
by  ordinary  analytical  methods,  but  micro- 
metric  analysis  of  the  eutectic  appearing  in 
a  photomicrograph  presents  most  accurate 


54 


MAKING 


STANDARDIZED      DENTAL      AMALGAM      ALLOY 


results.  This  is  accomplished  by  measure- 
ment of  the  eutectic  areas  with  a  planim- 
eter,  or  by  the  count  of  squares  method. 

Copper  is  unique  in  its  capacity  for 
absorbing  oxygen  and  furnace  gases,  hence 
the  use  of  the  electric  furnace  for  melting 


Figure  58  —  Conductivity  copper,  used  in 
the  manufacture  of  Crandall's  Scientifi- 
cally Tested  Non-Zinc  Alloy.  Note  its 
beautiful,  clear  structure,  as  compared 
with  coppers  containing  slight  impurities. 
Magnification  SOX. 


it  is  imperative,  as  all  effort  to  obtain  pure 
metals  avails  very  little  if  they  are  after- 
ward contaminated  by  melting  in  a  gas 
furnace. 

Figure  54  shows  copper  with  0.2  per 
cent  of  oxygen;  Figure  55  copper  with  a 
slight  amount  of  impurity  showing  core 
structure;  Figure  56  electrolytic  copper; 
Figure  57  another  impure  copper  with 
tree  structure  or  dendrites. 

The  copper  purchased  and  used  for 
Crandall's  Scientifically  Tested  Non-Zinc 
Alloy  is  of  that  highest  quality  known  as 
conductivity  copper;  its  beautiful  clear 
structure  is  shown  in  Figure  58  and 
Figure  59. 


Melting 

To  those  unfamiliar  with  the  manufac- 
ture of  dental  amalgam  alloys,  it  might 
now  appear  that,  having  assembled  the 
pure  metals,  it  would  be  a  simple  matter 
to  melt  them  together,  and  that  the  result- 
ing ingot  would  be  pure,  containing  silver, 
tin,  and  copper,  in  the  same  proportions 
which  were  originally  placed  in  the  crucible. 
Various  obstacles,  however,  prevent  this. 
If  the  metals  were  simply  melted  together, 
under  ordinary  conditions,  the  mass  would 
absorb  oxygen  with  a  resulting  partial 
oxidation  of  the  copper  and  tin  which 
would  entirely  nullify  the  exact  propor- 
tions originally  taken. 

Reducing  agents,  such  as  carbon,  prevent 
oxidation,  but  the  alloy  takes  up  some  car- 


Figure  59  —  Another  specimen  of  conduc- 
tivity copper.  The  black  spots  are  polish- 
ing and  etching  pits,  the  large  grains  are 
due  to  anneaUng.     Magnification  SOX. 


bon  and  the  benefit  of  this  addition  may 
certainly  be  questioned.  As  the  quantity 
taken  up  is  variable,  and  generally  un- 
known, we  prefer  to  eliminate  it  altogether. 
The  use  of  plumbago  or  clay  crucibles  is 


N 


MAKING 


STANDARDIZED       DENTAL       AMALGAM       ALLOY 


also  subject  to  criticism;  the  former  may 
impart  graphitic  carbon  and  the  latter 
iron  oxide. 

As  an  absolute  safeguard  from  any  possi- 
bility of  oxidation   and   to  eliminate  the 


Figure  60  shows  the  electric  furnace  used 
for  melting,  together  with  apparatus  for 
generating  and  purifying  hydrogen.  A 
pure  silica  rod  is  used  for  stirring  the  alloy 
during  its  melting. 


Figure  60  —  Melting  silver,  copper,  and  tin  in  a  closed  electric  furnace, 
under  hydrogen  gas. 


necessity  for  conjecture  as  to  the  effect  of 
ever-changing  quantities  of  carbon,  the 
metals  used  for  Crandall's  Scientifically 
Tested  Non-Zinc  Alloy  are  melted  in  a 
pure  silica  crucible,  in  an  enclosed  electric 
furnace,  under  pure  hydrogen  gas.  The 
hydrogen  gas  is  generated  simultaneously 
with  the  melting  of  the  alloy,  passing 
through  a  purifying  train,  and  flowing  over 
the  surface  of  the  metals  throughout  the 
melting.  No  heat  is  applied  to  the  crucible 
until  the  air  has  been  replaced  by  hydrogen. 


Dental  amalgam  alloys  are  frequently 
made  by  placing  silver  and  copper  in  the 
furnace  first,  adding  the  tin  after  these  are 
melted.  It  requires  a  high  degree  of  heat 
to  melt  the  silver  and  copper  alone  and 
various  alterations  take  place  at  this  tem- 
perature which  are  not  conducive  to  the 
formation  of  a  homogeneous  mass  upon 
subsequent  addition  of  the  tin.  In  order 
to  prevent  oxidation,  volatilization,  and 
other  complications,  we  alloy  at  as  low  an 
effective  temperature  as  possible.    The  tin, 


[56] 


MAKING      A      STANDARDIZED       DENTAL      AMALGAM       ALLOY 


melting  at  232°  C,  is  introduced  into  the 
electric  furnace  first,  and  copper  is  added 
over  a  rising  temperature  gradient  deter- 
mined by  pyrometric  methods.  There- 
upon is  formed  the  copper-tin  soHd  solution 
which  is  converted  into  the  correct  ternary 
alloy  by  the  addition  of  the  silver.  At  no 
time  is  the  melting  point  of  copper  or  silver 
approached  within  several  hundred  degrees. 

Throughout  the  melting  of  Crandall's 
Scientifically  Tested  Non-Zinc  Alloy,  met- 
allographic  control  is  maintained  with 
respect  to  fusion  period  and  maximum 
temperature;  temperature  gradient,  as 
observed  by  means  of  the  thermo-couple, 
with  Siemens-Halske  galvanometer  and 
adjusted  by  a  critical  point  rheostat;  the 
rate  of  hydrogen  flow,  as  affecting  oxidation 
and  reduction  reactions;  and  homogeneity 
through  mechanical  agitation. 

Casting 

When  the  galvanometer  records  the 
casting  temperature,  Crandall's  Scientifi- 
cally Tested  Non-Zinc  Alloy  is  run  into 
molds  in  an  atmosphere  of  hydrogen  and 
is  cooled  in  a  manner  found  to  promote 
desirable  physical  qualities. 

Filing 

As  the  undue  heat  generated  by  friction 
in  some  cutting  devices,  produces  unde- 
sirable physical  changes  in  alloy,  anneahng 
it  to  an  undetermined  extent,  Crandall's 
Scientifically  Tested  Non-Zinc  Alloy  is 
divided  by  hand  files  used  in  specially  con- 
structed machines.  These  are  run  so  slowly 
that  the  generation  of  heat  sufficient  to 
cause  physical  changes  in  the  alloy  is 
avoided. 

The  filings  produced  by  this  method  are 
rough  and  jagged  in  form,  and  offer  a 
bright,  clean  surface  to  the  attack  of  mer- 


cury. The  size  of  the  filings  has  been 
carefully  determined  to  produce  the  maxi- 
mum of  strength  in  the  undissolved 
integral  unit,  while  permitting  careful 
adaptation  at  the  margins. 

Annealing 

To  anneal  a  small  amount  of  alloy,  such 
an  amount  as  a  test  tube  would  contain 
for  instance,  is  a  simple  matter.  It  can  be 
brought  to  the  desired  temperature  im- 
mediately, maintained  at  that  point  for 
the  desired  period,  and  cooled  at  once. 

To  obtain  this  definite  result  with  the 
comparatively  large  quantities  of  alloy 
which  must  be  handled  in  a  manufacturing 
laboratory  involves  problems  which  have 
been  overcome  by  our  method  of  anneahng 
Crandall's  Scientifically  Tested  Non-Zinc 
Alloy.  The  continued  and  indefinite  an- 
nealing which  would  be  produced  by  slowly 
bringing  the  alloy  to  the  desired  tempera- 
ture and  by  slow  coohng  is  avoided  by  a 
method  which  brings  the  whole  amount  of 
alloy  immediately  to  the  desired  tempera- 
ture. It  is  maintained  at  this  point,  with- 
out fluctuation  to  a  higher  or  lower  point, 
for  a  definite  period  of  time,  during  which 
the  alloy  is  kept  constantly  in  motion.  The 
return  to  room  temperature  is  quickly  made. 

Formula 

The  balancing  principle  is  generally  con- 
ceded to  be  the  correct  one  for  combining 
the  dental  amalgam  alloj^  metals  in  such 
proportions  that  shrinkage  is  eliminated 
and  a  minimum  and  controlled  amount  of 
expansion  is  obtained.  This,  of  course, 
precludes  the  use  of  a  formula,  or  we  might 
say  necessitates  the  determination  of  a 
formula  for  every  lot  of  metals  obtained. 

Testing 

After  remelting,  refining,  and  testing  a 
lot  of  metals,  a  sample  melt  of  fifty  ounces 


[57] 


MAKING 


STANDARDIZED       DENTAL       AMALGAM       ALLOY 


is  made  up  into  alloy  and  sent  to  Dr. 
Crandall  for  his  test.  This  alloy  is  amal- 
gamated by  him  and  subjected  to  micro- 
micrometer  tests.  If  it  does  not  prove  to 
be  desirably  balanced,  but  shows  shrinkage 
or  undue  expansion,  he  corrects  the  per- 
centage error  which  usuallj'^  does  not 
exceed  0.1  per  cent. 

When  the  alloy  meets  with  his  approval 
Dr.  Crandall  furnishes  us  with  a  certificate 
of  his  tests,  showing  the  date  of  testing, 
setting  or  hardening  period,  expansion  in 
twenty-five  thousandths  of  an  inch,  and 
the  parts  of  mercury  which  should  be  used 
to  obtain  this  expansion. 

The  whole  lot  of  silver  is  then  made  up 
in  exactly  the  same  proportions  as  the 
sample  melt  which  has  been  tested  and  the 
information  contained  in  the  certificate 
given  us  by  Dr.  Crandall  is  copied  on  a 
certificate  which  is  attached  to  everj^  bottle 
of  Crandall's  Scientifically  Tested  Non- 
Zinc  Alloy  which  is  put  up  from  the  lot 
tested. 

Research  Laboratory  Tests 

Thermal  analysis  is  an  invaluable  aid  in 
research  and  enables  us  to  verify  or  refute 
the  claims  made  for  alloys  received  by  our 
laboratory'.  It  has  been  found  that  asser- 
tions as  to  chemical  composition,  definite 
formula,  annealing  conditions,  and  other 
claims,  are  often  entirely  unsubstantiated. 
For  instance,  an  alloy  bearing  the  definite 
formula,  "Ag-jSnCu,"  and  "aged  20  min- 
utes over  water  at  100°  C,"  shrunk  upon 
amalgamation,  and  showed  evidence  of 
incorrect  annealing.  This  alloy  did  not 
anah'ze  for  AgoSnCu,  and  a  photomicro- 
graph showed  the  eutectic  structure  of 
Figure  61,  which  was  further  verified  b}^ 
the  long  eutectic  halt  in  the  cooling  curve 
obtained  by  thermal  analysis. 


In  order  to  indicate  the  status  of  research 
upon  ternar}'  compounds  the  statement  of 
the  eminent  metallographist,  Dr.  Rosen- 
hain,  is  quoted: 

"Unfortunately  the  difficulty  of  making 
a  complete  metallographic  study  of  a  sys- 


Figure    61  —  Eutectic   structure    of   alloy 
represented  as  Ag-SnCu. 

tern  of  alloy's  increases  very  rapidly  with 
the  number  of  component  metals;  for  fifty 
determinations  required  for  the  elucidation 
of  a  binary  system  of  alloj^s,  1250  would  be 
required  for  a  system  of  three  metals, 
while  no  attempt  at  the  complete  system- 
atic study  of  a  quaternary  system  (of  four 
metals)  has  yet  been  made,  but  for  corre- 
sponding completeness  over  30,000  deter- 
minations would  be  needed.  In  the  case 
of  a  ternary  system  (of  three  metals)  it  is 
still  possible  to  employ  a  graphic  repre- 
sentation; the  concentration  of  a  system 
of  ternary  alloys  may  be  plotted  in  the 
form  of  an  equilateral  triangle,  each  corner 
representing  one  of  the  pure  component 
metals;  each  side  of  the  triangle  then  repre- 
sents one  of  the  three  limiting  binary 
systems,  while  the  position  of  any  point 
within   the   triangle   represents   the    com- 


[58] 


MAKING      A      STANDARDIZED      DENTAL      AMALGAM      ALLOY 


position  of  an  alloy  of  a  ternary  system, 
on  the  principle  of  trilinear  co-ordinates. 
Upon  this  equilateral  triangle  as  a  base, 
the  'equilibrium  diagram'  can  be  erected 
as  a  three  dimensional  model,  ordinates 
representing  temperature  being  erected 
upon  each  point  of  the  area  of  the  triangle. 
A  few  such  equilibrium  models  of  ternary 


systems  have  been  more  or  less  completely 
determined,  but  the  field  is  still  largely 
unexplored.  It  is  interesting  to  note  how- 
ever, that  no  tri-metallic  compound  has  yet 
been  discovered." 

The  location  of  Crandall's  Scientifically 
Tested  Non-Zinc  Alloy  upon  the  ternary 
diagram  is  shown  in  Figure  62. 


3EGINNING  OF  PERITECTIC 
ABOUT  HERE 


CRANDALL'S  SCIENTIFICALLY 
TESTED  NON-ZINC  ALLOY 

26.9%  Sn   in   AG3SN 


25%   Sn  end  OF  PERITECTIC  AT  480 


SOLUBILITY    DECREASES   TO 

SOME  20%  Sn  at  low 

TEMPERATURES 


28.2%  Cu   IN   EUTECTIC 


SATURATION    LIMIT  Cu   IN 

AG    SOLID    AT    EUTECTIC 

TEMPERATURE  779° 


Figure  62  —  Ternary  diagram  showing  the  location  of  Crandall's 
Scientifically  Tested  Non-Zinc  Alloy. 


[59] 


Instruments,  Materials  and  Appliances 

used  in  the 

Crandall  Method  of  Amalgam 
Restoration 

IN  the  following  pages  instruments,  materials,  and  appliances 
which  have  been  developed  by  Dr.  Crandall  or  have  been 
designed  to  meet  his  requirements  are  shown.  To  these  have  been 
added  amalgam  condensing  instruments  designed  by  Dr.  Prime 
and  amalgam  carving  instruments  designed  by  Dr.  Frahm. 

An  equipment  may  be  selected  from  these  pages  which  will 
fully  meet  the  demands  of  a  standardized  amalgam  technic  and, 
in  all  cases,  the  Clev-Dent  standard  of  quality  has  been  maintained. 


Crandall  Demonstrating  Case 

THIS  case  has  been  devised 
as  an  aid  in  explaining  to 
patients  the  desirabihty  of 
amalgam  restorations  as  com- 
pared to  inferior  work.  It  is 
a  small  leather  case,  velvet 
lined,  with  space  for  twelve 
steel  rings  which  are  used  to 
hold  teeth  with  various  forms 
of  cavity  preparation,  amalgam 
restorations,  and  other  features 
of  the  work  which  it  is  desired 
to  bring  to  the  patient's 
attention. 

The  teeth  are  not  supplied 
with  the  case,  but  may  be  pre- 
pared by  each  dentist  with  a 
view  to  meeting  the  particular 
needs  of  his  practice. 

The  case,  shown  here,  con- 
tains restorations  which  include 
nearly  all  of  the  forms  usually 
encountered  in  practice,  includ- 
ing several  restorations  of  the  entire  crown,  such  as  A.     At  B  is  shown  the 
cavity  preparation  for  an  amalgam  crown,  at  C   a  cavity  preparation  in  the 
medio-occlusal  surfaces  of  an  upper  molar.    At  D  are  five  extracted  teeth  which 
have  been  lost  because  of  the  poor  adaptation  of  gold  crowns. 


60 


CrandalFs  Scientifically 
Tested   Non-Zinc    Alloy 

Authoritative  information  regarding  the 
effect  of  zinc  and  overaging  on  dental 
alloys  has  long  been  accessible,  but 
dentists  have  failed  to  demand  an  alloy 
made  to  conform  to  the  highest  standards  and 
have  even  been  content  with  unbalanced  alloys 
because  of  their  plastic,  easy-working  qualities. 
The  manufacturer  has  been  content  to  deal  in 
glittering  generalities  in  describing  his  alloys, 
avoiding  definite  facts  and  figures,  specifica- 
tions, and  tests. 


5  OZ.  TROY 


SCIENTIFICAULY 
TESTED 

NON-ZINC 
ALLOY 


^leV-DENL 


The  Cleveland 


U.S.A. 


Contrary  to  this  plan,  investi- 
gation of  all  methods  of  alloy 
making  has  preceded  the  manu- 
facture of  Crandall's  Scientifically 
Tested  Xon-Zinc  Alloy  and  fullest 
advantage  has  been  taken  of  all 
authoritative  information  obtain- 
able. Much  of  original  research 
has  confirmed  or  rejected  various 
methods  and  has  evolved  new 
refinements  of  the  process. 

In  addition  to  chemical  and 
metallographic  tests  of  materials 
and  micrometer  tests  of  the 
finished  product  made  in  our  own 
laboratories,  every  lot  of  Cran- 
dall's Scientifically  Tested  Non- 
Zinc  Alloy  is  tested  by  Dr. 
Crandall. 


[61] 


Crandall's  Scientifically  Tested  Non-Zinc  Alloy 


CERTIFICATE  OF  TEST 

Spencer,   Iowa..._<~r- *^.....  ..19' 

This  certifies  that  I  have  tested  Lot  No.  /^../P./.. 
manufacturecl...ifr^7.'rv/^^/'^..of  Crandall's  Scientifically 
Tested  Non-Zinc  Alloy  and  find  the  following  results: 

With  10  parts  alloy  ..v^...- parts  mercury  should  be 
used.     Expansion  is..^..  / 25000  of^n  inch. 

Setting  ..M4^.^ 


CERTIFICATE  OF  TEST 

Spencer,   \oyNa...^*^^h^.././. W..'^.. 

This  certifies  that  I  have  tested  Lot  Wor-^/D  /^/.. 
manufactured-.-7^..T'-.yr""/^-of  Crandall's  Scientifically 
Tested  Non-Zinc  Alloy  and  find  the  following  results: 

With  10  parts  alloy  ___// parts  mercury  should  be 

used.     Expansion  is.-?!^.  / 25000  of  an  inch. 

Setting  i/^v^^^r^trT?:::^::     ^.^^lj^^^^..<r.rr.r^^ 


Dr.  Crandall  certifies  to  his  test  of  every  lot  of  the  alloy,  furnishing  us  with  a 
certificate,  showing  the  setting  qualities,  expansion  in  twenty-five  thousandths 
of  an  inch,  and  the  parts  of  mercury  to  be  used  to  obtain  this  amount  of  expan- 
sion. Facsimiles  of  two  of  these  certificates  are  shown  on  this  page.  The  date 
of  manufacture  is  also  shown  on  each  certificate.  The  information  contained 
in  this  certificate  is  transferred  to  the  label  of  every  bottle  of  Crandall's  Scien- 
tifically Tested  Non-Zinc  Alloy  put  up  from  the  lot  tested. 


[62] 


Crandall's    Scientifically    Tested 
Non-Zinc  Alloy 

IN  addition  to  the  blue  label  which  serves 
as  a  ready  means  of  identification  of 
Crandall's  Scientifically  Tested  Non-Zinc 
Alloy,  every  bottle  of  this  alloy  bears  on  its 
reverse  side  a  certificate  label  which  contains 
the  information  certified  to  by  Dr.  Crandall 
in  his  test  of  the  alloy. 

It  would  be  quite  possible  for  a  dentist  to 
purchase  a  quantity  of  alloy  and  after  retain- 
ing it  for  a  long  time,  to  return  it  to  his  dealer 
who  would,  not  knowing  its  age,  sell  it  again. 
The  user  of  Crandall's  Scientifically  Tested 
Non-Zinc  Alloy  is  fully  protected  from  the 
possibility  of  using  an  overaged  alloy  by  the 
date  of  manufacture  which  appears  on  every 
package,  and  from  loss  of  alloy  overaged  in 
his  own  hands,  by  our  offer  to  exchange, 
without  charge,  all  alloy  on  hand  one  year 
from  the  date  of  its  manufacture. 

Dr.  Crandall's  Certificate  of  the  exact 
amount  of  expansion  and  the  parts  of  mer- 
cury to  be  used  with  the  particular  lot  of  alloy 
tested  places  in  the  dentist's  hands  informa- 
tion which  is  invaluable  in  obtaining  the 
definite  and  dependable  results  which  he 
should  expect  from  a  correct  amalgam  technic. 


MERCURY 
KE-DlSTtLI^D 

m^  Dental  Ufi,  k 

ClSVELAMD,  OHIO 


Clev-Dent  Redistilled 
Mercury 

A  CHEMICALLY  pure  mercury  which  is 
guaranteed  not  to  contain  foreign  metals 
which  might  disturb  the  proportions  of  an 
accurately  balanced  alloy. 

This  is  put  up  in  jugs  containing  one  pound, 
as  shown  in  the  illustration,  also  in  bottles  and 
cones,  containing  one-quarter  pound  each. 


63 


Crandall  Seamless 
Copper  Matrix   Bands 


® 


An  assortment  of  seamless  copper  bands  of  suitable  size  for  use  as  matrices 
in  making  full  or  partial  amalgam  crowns  as  described  by  Dr.  Crandall  on  page 
16.  The  illustration  shows  the  actual  circumference  of  the  bands  and  the  line 
at  the  right  shows  the  length  when  cut.    The  height  of  bands  is  8  mm. 

These  bands  are  put  up  in  boxes  containing  twenty-five  bands  of  one  size 
and  in  compartment  boxes  containing  one  hundred  bands  in  the  following 
assortment:  5  each,  Nos.  1,  2,  3,  6,  13,  14;  6  each,  Nos.  4,  5,  7; 
8  each,  Nos.  8,  12;  12  each,  Nos.  9,  10,  11. 

Wedgwood  Mortar  and  Pestle 

DR.  CRANDALL  recommends  a  pestle 
of  sufficient  size  and  correct  shape  to 
touch  all  points  in  the  mortar  for  trit- 
urating alloy.  This  mortar  and  pestle 
have  been  carefully  designed  to  meet  his 
requirements.  Another  view  is  shown  on 
page  39,  Figure  40. 


[64] 


Crandall  Alloy  Balance 


Patented  —  June  6,  1916 


A  SMALL  well  made  balance,  indicating  weight  in  parts.  Its  accuracy  is 
quite  sufficient  for  determining  proportions  of  mercury  and  alloy  so  that 
the  sloppy  excess  of  mercury,  which  is  likely  to  disturb  the  balance  of  the 
metals  when  expressed,  is  avoided.  Accurate  judgment  of  the  amount  of 
amalgam  required  for  fillings  of  various  sizes,  is  soon  acquired  with  the  help 
of  this  balance  and  a  decided  economy  in  the  use  of  alloy  is  the  result. 

The  balance  is  most  conveniently  used  by  setting  one  of  the  sliding  weights 
on  the  arm  at  the  number  of  parts  of  alloy  required  and  slowly  sifting  alloy 
from  the  bottle  into  the  pan  until  it  is  balanced.  After  the  alloy  is  poured  into 
the  mortar,  without  disturbing  the  first  weight,  set  the  second  weight  for  the 
additional  parts  of  mercury  required  and  pour  in  mercury  to  balance. 


Crandall  Copper 
Matrix  Metal 


For  making 
the  tied  copper 
matrices  de- 
scribed by  Dr. 
Crandall  on 
pages  13  to  15. 

Each  pack- 
age contains  five 
sheets  of  36  ga. 
copper,  six  by 
three  inches. 


Craadall   Copper   Matrix   Metal 


i-nX  SHCETS-SIK   BV  THPEE  I^Ci^^S 
N'>    •f'   B.  ^Y  S.  QX^  F 


The  Cleveland   Dental  Mfj*.  Co. 


N 


Woodbury-Crandall  Instruments 
for  Cavity  Preparation 


t 


t  ^^ 


Design  Patent  Applied  for 

1 


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95 

95 

80 

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12 

14 

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23 

2 

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5 

5 

10 

10 

10 

10 

6 

6 

6 

6 

12 

12 

12 

12 

L 

R 

L 

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3 

4 

5 

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7 

8 

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[66] 


Woodbury-Crandall  Instruments  for 
Cavity  Preparation 

THE  forms  which  make  up  this  new  set  of  instruments  for  cavity  prepara- 
tion have  been  carefully  chosen  and  adapted  by  Dr.  Charles  E.  Woodbury 
and  Dr.  Walter  G.  Crandall  from  some  of  the  best  known  and  generally 
approved  sets  of  cutting  instruments.  Their  form  has  been  modified  some- 
what and  a  radical  change  has  been  made  by  shortening  the  neck,  bringing 
the  handle  much  nearer  the  cutting  edge  of  the  instrument  and  affording  a 
very  firm  finger  grasp  with  increased  leverage  and  control.  The  diameter  of 
the  handles  of  the  instruments  varies,  being  carefully  adjusted  to  balance  the 
width  of  the  cutting  edge.  The  instruments  are  practically  universal  in  their 
application  and  include  all  the  necessary  forms  for  the  preparation  of  cavities 
on  any  surface  of  the  teeth. 

For  the  most  efficient  use  of  these  instruments,  we  suggest  the  duplication 
of  those  forms  oftenest  in  use,  so  that  an  instrument  need  never  be  used  after 
it  has  been  sufficiently  dulled  to  cause  pain.  An  economical  and  time  saving 
arrangement  may  be  made  with  us  for  sharpening  these  and  all  other  hand 
operating  instruments  for  a  fixed  sum  per  year. 

Nos.  1  and  2  are  hatchets  for  forming  angles  in  the  anterior  teeth. 

Nos.  3,  4,  and  5  are  contra  angle  hoes,  and  6  and  7  are  right  angle  hoes, 
instruments  of  the  widest  application  in  cavity  formation. 

Nos.  8,  9,  10,  and  11  are  right  and  left  angle  forming  instruments  designed 
especially  for  carrying  out  the  sharp  line  angles  in  cavities  in  the  anterior  teeth. 

Nos.  12,  13,  14,  and  15  are  right  and  left,  mesial  and  distal  gingival  margin 
trimmers. 

Nos.  16,  17,  18,  19,  20,  21,  26,  and  27  are  right  and  left  spoon  excavators. 

Nos.  22,  23,  24,  and  25  are  right  and  left  enamel  hatchets  for  breaking 
down  enamel  and  shaping  cavity  walls  in  bicuspids  and  molars,  one  of  each 
pair  is  marked  with  a  ring  to  distinguish  the  direction  of  cut  without  examina- 
tion of  the  cutting  edge.  Nos.  28,  29,  30,  and  31  are  front  and  back  cut  enamel 
cutting  chisels.  One  of  each  pair  is  marked  with  a  ring  so  that  those  which 
cut  on  the  back  may  be  distinguished  from  those  which  cut  on  the  face,  with- 
out examination  of  the  cutting  edge.  These  enamel  instruments  have  a  special 
temper,  differing  from  that  of  the  other  instruments  of  the  set.  On  account 
of  their  special  hardness,  they  not  only  are  better  suited  for  cutting  enamel 
but  will  hold  their  edge  longer. 

Nos.  32  and  33  are  special  instruments  for  cutting  mesially  and  distally 
in  molar  cavities  which  are  difficult  of  access. 

Nos.  34  and  35  are  finishing  knives  designed  for  finding  and  removing 
overlaps  along  the  gingival  margins  of  fillings  on  the  proximal  surfaces. 


[67] 


Prime  Amalgam  Instruments 

Patent  Applied  for 

AYith  the  advances  recently  made  in  the  development  of 
amalgam  technic,  the  necessity  for  instruments  which  may 
be  used  with  the  mallet  to  carry  pressure  or  force  directly  into 
the  angles  of  the  cavity  has  become  apparent.  Dr.  J.  M.  Prime 
has  met  this  need  by  designing  the  set  of  amalgam  condensing 
instruments  shown  here. 

These  instruments  are  necessarily  heavy  in  construction, 
to  avoid  any  tendency  to  spring  under  pressure.  The  bayonet 
is  sufficiently  long  to  permit  of  access  to  the 
distal  portion  of  posterior  teeth,  and  the 
opposite  end  of  the  instrument  has  a  cor- 
responding offset  so  that  force  applied  to 
the  end  of  the  handle  with  the  mallet  will 
be  in  direct  line  with  the  condensing  point. 


[68] 


K.'^f] 


Prime 
Vmalgam  Instruments 


All  of  the  condensing  points  are  con- 
cave that  they  may  grasp  and  force 
forward  the  amalgam,  eliminating 
the  clogging  feature  so  inconvenient 
in  serrated  instruments. 

Instruments  No.  11  and  No.  12  have  a 
concave  outline  as  well  as  a  concave  con- 
densing surface.  This  adapts  them  for  use 
on  the  buccal  surface  of  the  teeth,  where 
the  convexity  of  the  surface  necessitates 
the  use  of  an  instrument  of  this  form  to 
produce  equal  pressure  over  all  of  the  mar- 
gins simultaneously. 

Instrument  No.  13  is  used  for  condens- 
ing amalgam  into  cavities  occurring  at  the 
buccal  groove,  also  providing  equal  dis- 
tribution of  pressure  into  the  angles  of 
the  cavity. 

The  trimming  knives  Nos.  14  and  15 
are  used  for  removing  small  particles  of 
amalgam  overhanging  at  the  gingival  mar- 
gins, for  carving  the  correct  anatomical 
form  at  the  gingival  and  restoring  the  inter- 
proximal space.  These  instruments  are  so 
delicate  that  they  will  detect  a  very  slight 
overhang,  which  may  afterward  be  removed 
with  finishing  files  or  strips. 


69 


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30 

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8 


3 

6 

20 

20 

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16 

Crandall  Amalgam  Instruments 

THESE  instruments  have  been  designed  by  Dr.  Crandall  to  fit  into 
the  proximal  and  occlusal  portions  of  such  cavities  as  are  usually 
made  in  bicuspid  and  molar  teeth  for  amalgam  fillings.  As  wUl  be 
noted  from  the  illustration,  they  have  shortened  shanks  bringing  the 
working  point  of  the  instrument  closer  to  the  grasp  which  controls  it 
and  affording  great  leverage  and  very  accurate  control.  When  used  as 
pluggers  to  carry  a  mass  of  amalgam  and  condense  it  under  heavy 
hand  pressure,  supplemented  by  mallet  force,  they  will  produce  the 
greatest  possible  density  and  strength  in  the  filling. 

Xos.  1  to  7  are  for  cavities  in  the  inferior  teeth  which  are  inaccessible 
to  the  bayonet  shaped  instruments,  Xos.  8  to  1-i. 

Xos.  7  and  14  are  especially  valuable  as  their  size  allows  them  to 
condense  a  mass  of  amalgam  over  all  the  margins  of  the  cavity,  simul- 
taneously, thus  avoiding  the  movement  away  from  some  portions  of 
the  margins  which  is  always  produced  by  the  use  of  small  pluggers. 

X'os.  15  and  16  are  amalgam  formers  for  reducing  the  excess  of 
amalgam  to  the  cavity  margins  and  for  preliminary  carving  in  the 
restoration  of  the  natural  tooth  form. 


§_s:j 


III 


Frahm   Carving 
Instruments 


THE  occlusal  surface  of  amalgam  restorations  is  easily  and  correctly 
carved  with  these  instruments  so  that  normal  masticatory  form 
and  function  are  restored.  There  are  four  sets  of  the  instruments,  each 
made  up  of  a  straight  instrument,  a  right,  and  a  left.  The  four  sets 
differ  from  one  another  in  the  cutting  angle  of  the  blades,  which  is  75°, 
90,°  105°,  or  120°.  These  angles  will  take  care  of  all  the  varieties  of 
fissure  formations  found  in  the  human  teeth.  The  set  illustrated  has 
cutting  blades  at  an  angle  of  105°.  The  other  angles  are  shown,  in 
comparison  with  this,  in  the  drawing  at  their  right. 

Dr.  F.  W.  Frahm,  who  supplied  the  patterns  for  these  instruments, 
has  also  furnished  us  with  the  following  technic  for  their  use  in  the  mouth 
or  upon  models: 

"In  the  case  of  the  occlusal  surface  of  an  inferior  first  molar  involv- 
ing all  the  fissures:  Place  the  blade  of  the  straight  instrument  (No.  1) 
at  the  point  'a'  where  the  buccal  fissure  joins  the  central  fissure, 
embedding  the  blade  in  the  wax  or  amalgam  until  the  blades  touch 
the  margin  of  the  cavity.  Draw  the  instrument  forward,  allowing  both 
sides  of  the  blade  to  cut  to  their  full  depth,  until  the  medio-occlusal 
marginal  pit  'b'  is  reached.  Then  using  either  the  right  or  the  left 
instrument,  according  to  the  tooth,  place  it  in  the  fossa  end  of  the 
buccal  fissure  'a,'  pass  it  to  the  buccal  side,  following  the  course  of 
this  fissure,  releasing  the  pressure  as  'c'  is  neared.  Then,  using  the 
straight  instrument,  cut  from  'a'  to  'd'  with  a  push  cut;  from  this 
point,  push  the  instrument  distally  to  the  juncture  of  the  disto-buccal 
and  distal  fissures  'f.'  Select  the  proper  right  or  left  instrument,  as 
indicated,  place  it  at  'd'  and  draw  lingually  to  make  that  fissure,  then 
with  the  same  instrument  placed  at  'b'  draw  to  'i'  and  'j'  to  finish 
the  medio-marginal  pit.     Then  place  it  at  'f  and  draw  to  'g'  and  'h.' 

"When  passing  a  triangular  ridge  the  pressure  should  always  be  released  somewhat,  but  always 
start  in  a  pit  and  end  in  another  with  a  steady  clean  cut.  In  case  of  lingual  or  buccal  fissures  the 
pressure  should  be  released  when  the  coronal  ridge  is  neared  or  crossed. 

"The  angle  of  the  set  of  instruments  to  be  used  on  the  tooth  should  be  selected  to  conform  to  the 
fissures  found  in  other  teeth  of  the  same  mouth. 

"Supplemental  fissures  may  be  made  by  placing  one  edge  of  the  blade  on  the  material  and  gouging 
slightly  until  they  are  the  desired  depth. 

"The  cutting  should  be  done  with  a  firm  hand  and  clean  cut.  The  use  of  the  instruments  is  only 
limited  by  the  anatomical  variation  of  the  tooth." 


[71] 


Crandall  Carving 
Instruments 

Design  Patent  Applied  For 


g-ii 


11 

12 

85 

14 
85 

14 
85 

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5 

6 

6 

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23 

2 

18 

3 

18 

4 

For  carving  and  finishing  amalgam 
restorations,  so  that  the  natural 
form  of  the  occluding  and  other 
surfaces  is  fully  re-established,  Dr. 
Crandall  has  designed  these  four 
instruments  and  advocates  their 
use  in  connection  ^-ith  other  in- 
struments chosen  from  the  cavity 
preparation  set  and  the  amalgam 
set  shown  on  preceding  pages. 

Nos.  15  and  16  from  the  Amalgam 
Instruments  are  used  for  reducing 
the  excess  of  amalgam  upon  occlu- 
sal surfaces  to  the  point  where  the 
final  car^'ing  and  reproduction  of 
natural  detail  may  be  taken  up  by 
the  Instruments  following. 

Nos.  28,  29,  33  and  34  from  the 
Woodbur>"-Crandall  set  are  used 
for  shaping  the  cusp  surfaces  and 
planes. 

Nos.  10  and  11  from  the  Wood- 
bury-Crandall  set  are  for  push 
cutting,  and  Nos.  1,  2,  3  and  4, 
shown  above,  for  pull  cutting,  in 
forming  sulci  and  pits. 


7D 


m 


Prime 

Condensing 

Mallet 

This  mallet  was  designed 
by  Dr.  J.  M.  Prime  for 
affording  the  pressure  nec- 
essary to  condense  amal- 
gam. The  illustration 
shows  the  actual  length  and 
diameter  of  the  head.  The 
hickon,-  handle  is  nine 
inches  long,  the  head  weighs 
five  ounces. 

A  brass  tube,  heavily  nickel- 
plated  and  filled  with  lead 
forms  the  head  of  this 
mallet.  The  ends  are  faced 
with  leather,  inset  so  that 
it  covers  the  entire  face  of 
the  mallet  and  prevents  the 
instrument  from  coming  in 
contact,  accidentally,  with 
the  metal  edge. 


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